diff --git a/Filelist b/Filelist
index f488839..343a2bd 100644
--- a/Filelist
+++ b/Filelist
@@ -273,6 +273,20 @@
 		src/libvterm/t/92lp1640917.test \
 		src/libvterm/t/harness.c \
 		src/libvterm/t/run-test.pl \
+		src/xdiff/xdiff.h \
+		src/xdiff/xdiffi.c \
+		src/xdiff/xdiffi.h \
+		src/xdiff/xemit.c \
+		src/xdiff/xemit.h \
+		src/xdiff/xhistogram.c \
+		src/xdiff/xinclude.h \
+		src/xdiff/xmacros.h \
+		src/xdiff/xpatience.c \
+		src/xdiff/xprepare.c \
+		src/xdiff/xprepare.h \
+		src/xdiff/xtypes.h \
+		src/xdiff/xutils.c \
+		src/xdiff/xutils.h \
 
 
 # source files for Unix only
diff --git a/runtime/doc/diff.txt b/runtime/doc/diff.txt
index d56aea7..6670f45 100644
--- a/runtime/doc/diff.txt
+++ b/runtime/doc/diff.txt
@@ -39,7 +39,9 @@
 then append the file name of the first argument to the directory name to find
 the file.
 
-This only works when a standard "diff" command is available.  See 'diffexpr'.
+By default an internal diff library will be used.  When 'diffopt' or
+'diffexpr' has been set an external "diff" command will be used.  This only
+works when such a diff program is available.
 
 Diffs are local to the current tab page |tab-page|.  You can't see diffs with
 a window in another tab page.  This does make it possible to have several
@@ -344,8 +346,9 @@
 
 The ">" is replaced with the value of 'shellredir'.
 
-The output of "diff" must be a normal "ed" style diff.  Do NOT use a context
-diff.  This example explains the format that Vim expects: >
+The output of "diff" must be a normal "ed" style diff or a unified diff.  Do
+NOT use a context diff.  This example explains the format that Vim expects for
+the "ed" style diff: >
 
 	1a2
 	> bbb
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index fca2e46..16aa422 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -2609,8 +2609,8 @@
 			{not in Vi}
 			{not available when compiled without the |+diff|
 			feature}
-	Expression which is evaluated to obtain an ed-style diff file from two
-	versions of a file.  See |diff-diffexpr|.
+	Expression which is evaluated to obtain a diff file (either ed-style
+	or unified-style) from two versions of a file.  See |diff-diffexpr|.
 	This option cannot be set from a |modeline| or in the |sandbox|, for
 	security reasons.
 
@@ -2657,11 +2657,31 @@
 		foldcolumn:{n}	Set the 'foldcolumn' option to {n} when
 				starting diff mode.  Without this 2 is used.
 
-	Examples: >
+		internal	Use the internal diff library.  This is
+				ignored when 'diffexpr' is set.  *E960*
+				When running out of memory when writing a
+				buffer this item will be ignored for diffs
+				involving that buffer.  Set the 'verbose'
+				option to see when this happens.
 
-		:set diffopt=filler,context:4
+		indent-heuristic
+                                 Use the indent heuristic for the internal
+                                 diff library.
+
+                algorithm:{text} Use the specified diff algorithm with the
+				internal diff engine. Currently supported 
+				algorithms are:
+				myers      the default algorithm
+				minimal    spend extra time to generate the
+					   smallest possible diff
+				patience   patience diff algorithm
+				histogram  histogram diff algorithm
+
+	Examples: >
+		:set diffopt=internal,filler,context:4
 		:set diffopt=
-		:set diffopt=filler,foldcolumn:3
+		:set diffopt=internal,filler,foldcolumn:3
+		:set diffopt-=internal  " do NOT use the internal diff parser
 <
 				     *'digraph'* *'dg'* *'nodigraph'* *'nodg'*
 'digraph' 'dg'		boolean	(default off)
diff --git a/src/Make_cyg_ming.mak b/src/Make_cyg_ming.mak
index 16cd712..2308135 100644
--- a/src/Make_cyg_ming.mak
+++ b/src/Make_cyg_ming.mak
@@ -166,6 +166,25 @@
 ifndef CROSS_COMPILE
 CROSS_COMPILE =
 endif
+
+# About the "sh.exe" condition, as explained by Ken Takata:
+#
+# If the makefile is executed with mingw32-make and sh.exe is not found in
+# $PATH, then $SHELL is set to "sh.exe" (without any path). In this case,
+# unix-like commands might not work and a dos-style path is needed.
+# 
+# If the makefile is executed with mingw32-make and sh.exe IS found in $PATH,
+# then $SHELL is set with the actual path of sh.exe (e.g.
+# "C:/msys64/usr/bin/sh.exe").  In this case, unix-like commands can be used.
+# 
+# If it is executed by the "make" command from cmd.exe, $SHELL is set to
+# "/bin/sh". If the "make" command is in the $PATH, other unix-like commands
+# might also work.
+# 
+# If it is executed by the "make" command from a unix-like shell,
+# $SHELL is set with the unix-style path (e.g. "/bin/bash").
+# In this case, unix-like commands can be used.
+#
 ifneq (sh.exe, $(SHELL))
 DEL = rm
 MKDIR = mkdir -p
@@ -810,6 +829,23 @@
 	$(OUTDIR)/term_vterm.o
 endif
 
+# Include xdiff
+OBJ +=  $(OUTDIR)/xdiffi.o \
+	$(OUTDIR)/xemit.o \
+	$(OUTDIR)/xprepare.o \
+	$(OUTDIR)/xutils.o \
+	$(OUTDIR)/xhistogram.o \
+	$(OUTDIR)/xpatience.o
+
+XDIFF_DEPS = \
+	xdiff/xdiff.h \
+	xdiff/xdiffi.h \
+	xdiff/xemit.h \
+	xdiff/xinclude.h \
+	xdiff/xmacros.h \
+	xdiff/xprepare.h \
+	xdiff/xtypes.h \
+	xdiff/xutils.h
 
 ifdef MZSCHEME
 MZSCHEME_SUFFIX = Z
@@ -1055,6 +1091,23 @@
 $(OUTDIR)/term_vterm.o: libvterm/src/vterm.c $(TERM_DEPS)
 	$(CCCTERM) libvterm/src/vterm.c -o $@
 
+$(OUTDIR)/xdiffi.o: xdiff/xdiffi.c $(XDIFF_DEPS)
+	$(CC) -c $(CFLAGS) xdiff/xdiffi.c -o $(OUTDIR)/xdiffi.o
+
+$(OUTDIR)/xemit.o: xdiff/xemit.c $(XDIFF_DEPS)
+	$(CC) -c $(CFLAGS) xdiff/xemit.c -o $(OUTDIR)/xemit.o
+
+$(OUTDIR)/xprepare.o: xdiff/xprepare.c $(XDIFF_DEPS)
+	$(CC) -c $(CFLAGS) xdiff/xprepare.c -o $(OUTDIR)/xprepare.o
+
+$(OUTDIR)/xutils.o: xdiff/xutils.c $(XDIFF_DEPS)
+	$(CC) -c $(CFLAGS) xdiff/xutils.c -o $(OUTDIR)/xutils.o
+
+$(OUTDIR)/xhistogram.o: xdiff/xhistogram.c $(XDIFF_DEPS)
+	$(CC) -c $(CFLAGS) xdiff/xhistogram.c -o $(OUTDIR)/xhistogram.o
+
+$(OUTDIR)/xpatience.o: xdiff/xpatience.c $(XDIFF_DEPS)
+	$(CC) -c $(CFLAGS) xdiff/xpatience.c -o $(OUTDIR)/xpatience.o
 
 pathdef.c: $(INCL)
 ifneq (sh.exe, $(SHELL))
diff --git a/src/Make_mvc.mak b/src/Make_mvc.mak
index f329033..1131f2b 100644
--- a/src/Make_mvc.mak
+++ b/src/Make_mvc.mak
@@ -813,6 +813,24 @@
 !endif
 SUBSYSTEM_TOOLS = console
 
+XDIFF_OBJ = $(OBJDIR)/xdiffi.obj \
+	$(OBJDIR)/xemit.obj \
+	$(OBJDIR)/xprepare.obj \
+	$(OBJDIR)/xutils.obj \
+	$(OBJDIR)/xhistogram.obj \
+	$(OBJDIR)/xpatience.obj
+
+XDIFF_DEPS = \
+	xdiff/xdiff.h \
+	xdiff/xdiffi.h \
+	xdiff/xemit.h \
+	xdiff/xinclude.h \
+	xdiff/xmacros.h \
+	xdiff/xprepare.h \
+	xdiff/xtypes.h \
+	xdiff/xutils.h
+
+
 !if "$(SUBSYSTEM_VER)" != ""
 SUBSYSTEM = $(SUBSYSTEM),$(SUBSYSTEM_VER)
 SUBSYSTEM_TOOLS = $(SUBSYSTEM_TOOLS),$(SUBSYSTEM_VER)
@@ -1204,12 +1222,12 @@
 	tee/tee.exe \
 	GvimExt/gvimext.dll
 
-$(VIM).exe: $(OUTDIR) $(OBJ) $(GUI_OBJ) $(CUI_OBJ) $(OLE_OBJ) $(OLE_IDL) $(MZSCHEME_OBJ) \
+$(VIM).exe: $(OUTDIR) $(OBJ) $(XDIFF_OBJ) $(GUI_OBJ) $(CUI_OBJ) $(OLE_OBJ) $(OLE_IDL) $(MZSCHEME_OBJ) \
 		$(LUA_OBJ) $(PERL_OBJ) $(PYTHON_OBJ) $(PYTHON3_OBJ) $(RUBY_OBJ) $(TCL_OBJ) \
 		$(CSCOPE_OBJ) $(TERM_OBJ) $(NETBEANS_OBJ) $(CHANNEL_OBJ) $(XPM_OBJ) \
 		version.c version.h
 	$(CC) $(CFLAGS_OUTDIR) version.c
-	$(link) $(LINKARGS1) -out:$(VIM).exe $(OBJ) $(GUI_OBJ) $(CUI_OBJ) $(OLE_OBJ) \
+	$(link) $(LINKARGS1) -out:$(VIM).exe $(OBJ) $(XDIFF_OBJ) $(GUI_OBJ) $(CUI_OBJ) $(OLE_OBJ) \
 		$(LUA_OBJ) $(MZSCHEME_OBJ) $(PERL_OBJ) $(PYTHON_OBJ) $(PYTHON3_OBJ) $(RUBY_OBJ) \
 		$(TCL_OBJ) $(CSCOPE_OBJ) $(TERM_OBJ) $(NETBEANS_OBJ) $(CHANNEL_OBJ) \
 		$(XPM_OBJ) $(OUTDIR)\version.obj $(LINKARGS2)
@@ -1304,6 +1322,7 @@
 	$(MAKE) /NOLOGO -f Make_dos.mak nolog
 	$(MAKE) /NOLOGO -f Make_dos.mak $@.res
 	$(MAKE) /NOLOGO -f Make_dos.mak report
+	cat messages
 	cd ..
 
 ###########################################################################
@@ -1344,6 +1363,24 @@
 
 $(OUTDIR)/diff.obj:	$(OUTDIR) diff.c  $(INCL)
 
+$(OUTDIR)/xdiffi.obj:	$(OUTDIR) xdiff/xdiffi.c  $(XDIFF_DEPS)
+	$(CC) $(CFLAGS_OUTDIR) xdiff/xdiffi.c 
+
+$(OUTDIR)/xemit.obj:	$(OUTDIR) xdiff/xemit.c  $(XDIFF_DEPS)
+	$(CC) $(CFLAGS_OUTDIR) xdiff/xemit.c 
+
+$(OUTDIR)/xprepare.obj:	$(OUTDIR) xdiff/xprepare.c  $(XDIFF_DEPS)
+	$(CC) $(CFLAGS_OUTDIR) xdiff/xprepare.c 
+
+$(OUTDIR)/xutils.obj:	$(OUTDIR) xdiff/xutils.c  $(XDIFF_DEPS)
+	$(CC) $(CFLAGS_OUTDIR) xdiff/xutils.c 
+
+$(OUTDIR)/xhistogram.obj:	$(OUTDIR) xdiff/xhistogram.c  $(XDIFF_DEPS)
+	$(CC) $(CFLAGS_OUTDIR) xdiff/xhistogram.c 
+
+$(OUTDIR)/xpatience.obj:	$(OUTDIR) xdiff/xpatience.c  $(XDIFF_DEPS)
+	$(CC) $(CFLAGS_OUTDIR) xdiff/xpatience.c 
+
 $(OUTDIR)/digraph.obj:	$(OUTDIR) digraph.c  $(INCL)
 
 $(OUTDIR)/edit.obj:	$(OUTDIR) edit.c  $(INCL)
diff --git a/src/Makefile b/src/Makefile
index f2fafa4..d0cf956 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -1400,6 +1400,32 @@
 
 TERM_SRC = libvterm/src/*.c
 
+XDIFF_SRC = \
+	xdiff/xdiffi.c \
+	xdiff/xemit.c \
+	xdiff/xprepare.c \
+	xdiff/xutils.c \
+	xdiff/xhistogram.c \
+	xdiff/xpatience.c \
+
+XDIFF_OBJS = \
+	objects/xdiffi.o \
+	objects/xemit.o \
+	objects/xprepare.o \
+	objects/xutils.o \
+	objects/xhistogram.o \
+	objects/xpatience.o \
+
+XDIFF_INCL = \
+	xdiff/xdiff.h \
+	xdiff/xdiffi.h \
+	xdiff/xemit.h \
+	xdiff/xinclude.h \
+	xdiff/xmacros.h \
+	xdiff/xprepare.h \
+	xdiff/xtypes.h \
+	xdiff/xutils.h \
+
 ### Command to create dependencies based on #include "..."
 ### prototype headers are ignored due to -DPROTO, system
 ### headers #include <...> are ignored if we use the -MM option, as
@@ -1611,6 +1637,7 @@
 SRC =	$(BASIC_SRC) \
 	$(GUI_SRC) \
 	$(TERM_SRC) \
+	$(XDIFF_SRC) \
 	$(HANGULIN_SRC) \
 	$(LUA_SRC) \
 	$(MZSCHEME_SRC) \
@@ -1728,6 +1755,7 @@
 	$(WORKSHOP_OBJ) \
 	$(NETBEANS_OBJ) \
 	$(CHANNEL_OBJ) \
+	$(XDIFF_OBJS) \
 	$(WSDEBUG_OBJ)
 
 # The files included by tests are not in OBJ_COMMON.
@@ -2731,7 +2759,7 @@
 
 shadow:	runtime pixmaps
 	$(MKDIR_P) $(SHADOWDIR)
-	cd $(SHADOWDIR); ln -s ../*.[chm] ../*.in ../*.sh ../*.xs ../*.xbm ../gui_gtk_res.xml ../toolcheck ../proto ../libvterm ../vimtutor ../gvimtutor ../install-sh ../Make_all.mak .
+	cd $(SHADOWDIR); ln -s ../*.[chm] ../*.in ../*.sh ../*.xs ../*.xbm ../gui_gtk_res.xml ../toolcheck ../proto ../xdiff ../libvterm ../vimtutor ../gvimtutor ../install-sh ../Make_all.mak .
 	mkdir $(SHADOWDIR)/auto
 	cd $(SHADOWDIR)/auto; ln -s ../../auto/configure .
 	$(MKDIR_P) $(SHADOWDIR)/po
@@ -2915,7 +2943,7 @@
 objects/dict.o: dict.c
 	$(CCC) -o $@ dict.c
 
-objects/diff.o: diff.c
+objects/diff.o: diff.c $(XDIFF_INCL)
 	$(CCC) -o $@ diff.c
 
 objects/digraph.o: digraph.c
@@ -3229,6 +3257,27 @@
 objects/term_vterm.o: libvterm/src/vterm.c $(TERM_DEPS)
 	$(CCCTERM) -o $@ libvterm/src/vterm.c
 
+CCCDIFF = $(CCC_NF) $(ALL_CFLAGS)
+
+objects/xdiffi.o: xdiff/xdiffi.c $(XDIFF_INCL)
+	$(CCCDIFF) -o $@ xdiff/xdiffi.c
+
+objects/xprepare.o: xdiff/xprepare.c $(XDIFF_INCL)
+	$(CCCDIFF) -o $@ xdiff/xprepare.c
+
+objects/xutils.o: xdiff/xutils.c $(XDIFF_INCL)
+	$(CCCDIFF) -o $@ xdiff/xutils.c
+
+objects/xemit.o: xdiff/xemit.c $(XDIFF_INCL)
+	$(CCCDIFF) -o $@ xdiff/xemit.c
+
+objects/xhistogram.o: xdiff/xhistogram.c $(XDIFF_INCL)
+	$(CCCDIFF) -o $@ xdiff/xhistogram.c
+
+objects/xpatience.o: xdiff/xpatience.c $(XDIFF_INCL)
+	$(CCCDIFF) -o $@ xdiff/xpatience.c
+
+
 ###############################################################################
 ### MacOS X installation
 ###
diff --git a/src/diff.c b/src/diff.c
index c67654f..4c0792b 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -9,23 +9,32 @@
 
 /*
  * diff.c: code for diff'ing two, three or four buffers.
+ *
+ * There are three ways to diff:
+ * - Shell out to an external diff program, using files.
+ * - Use the compiled-in xdiff library.
+ * - Let 'diffexpr' do the work, using files.
  */
 
 #include "vim.h"
+#include "xdiff/xdiff.h"
 
 #if defined(FEAT_DIFF) || defined(PROTO)
 
 static int	diff_busy = FALSE;	/* ex_diffgetput() is busy */
 
 /* flags obtained from the 'diffopt' option */
-#define DIFF_FILLER	1	/* display filler lines */
-#define DIFF_ICASE	2	/* ignore case */
-#define DIFF_IWHITE	4	/* ignore change in white space */
-#define DIFF_HORIZONTAL	8	/* horizontal splits */
-#define DIFF_VERTICAL	16	/* vertical splits */
-#define DIFF_HIDDEN_OFF	32	/* diffoff when hidden */
+#define DIFF_FILLER	1	// display filler lines
+#define DIFF_ICASE	2	// ignore case
+#define DIFF_IWHITE	4	// ignore change in white space
+#define DIFF_HORIZONTAL	8	// horizontal splits
+#define DIFF_VERTICAL	16	// vertical splits
+#define DIFF_HIDDEN_OFF	32	// diffoff when hidden
+#define DIFF_INTERNAL	64	// use internal xdiff algorithm
 static int	diff_flags = DIFF_FILLER;
 
+static long diff_algorithm = 0;
+
 #define LBUFLEN 50		/* length of line in diff file */
 
 static int diff_a_works = MAYBE; /* TRUE when "diff -a" works, FALSE when it
@@ -36,22 +45,45 @@
 				      checked yet */
 #endif
 
+// used for diff input
+typedef struct {
+    char_u	*din_fname;  // used for external diff
+    mmfile_t	din_mmfile;  // used for internal diff
+} diffin_T;
+
+// used for diff result
+typedef struct {
+    char_u	*dout_fname;  // used for external diff
+    garray_T	dout_ga;      // used for internal diff
+} diffout_T;
+
+// two diff inputs and one result
+typedef struct {
+    diffin_T	dio_orig;     // original file input
+    diffin_T	dio_new;      // new file input
+    diffout_T	dio_diff;     // diff result
+    int		dio_internal; // using internal diff
+} diffio_T;
+
 static int diff_buf_idx(buf_T *buf);
 static int diff_buf_idx_tp(buf_T *buf, tabpage_T *tp);
 static void diff_mark_adjust_tp(tabpage_T *tp, int idx, linenr_T line1, linenr_T line2, long amount, long amount_after);
 static void diff_check_unchanged(tabpage_T *tp, diff_T *dp);
 static int diff_check_sanity(tabpage_T *tp, diff_T *dp);
 static void diff_redraw(int dofold);
-static int diff_write(buf_T *buf, char_u *fname);
-static void diff_file(char_u *tmp_orig, char_u *tmp_new, char_u *tmp_diff);
+static int check_external_diff(diffio_T *diffio);
+static int diff_file(diffio_T *diffio);
 static int diff_equal_entry(diff_T *dp, int idx1, int idx2);
 static int diff_cmp(char_u *s1, char_u *s2);
 #ifdef FEAT_FOLDING
 static void diff_fold_update(diff_T *dp, int skip_idx);
 #endif
-static void diff_read(int idx_orig, int idx_new, char_u *fname);
+static void diff_read(int idx_orig, int idx_new, diffout_T *fname);
 static void diff_copy_entry(diff_T *dprev, diff_T *dp, int idx_orig, int idx_new);
 static diff_T *diff_alloc_new(tabpage_T *tp, diff_T *dprev, diff_T *dp);
+static int parse_diff_ed(char_u *line, linenr_T *lnum_orig, long *count_orig, linenr_T *lnum_new, long *count_new);
+static int parse_diff_unified(char_u *line, linenr_T *lnum_orig, long *count_orig, linenr_T *lnum_new, long *count_new);
+static int xdiff_out(void *priv, mmbuffer_t *mb, int nbuf);
 
 #ifndef USE_CR
 # define tag_fgets vim_fgets
@@ -631,81 +663,290 @@
 	}
 }
 
+    static void
+clear_diffin(diffin_T *din)
+{
+    if (din->din_fname == NULL)
+    {
+	vim_free(din->din_mmfile.ptr);
+	din->din_mmfile.ptr = NULL;
+    }
+    else
+	mch_remove(din->din_fname);
+}
+
+    static void
+clear_diffout(diffout_T *dout)
+{
+    if (dout->dout_fname == NULL)
+	ga_clear_strings(&dout->dout_ga);
+    else
+	mch_remove(dout->dout_fname);
+}
+
 /*
- * Write buffer "buf" to file "name".
- * Always use 'fileformat' set to "unix".
- * Return FAIL for failure
+ * Write buffer "buf" to a memory buffer.
+ * Return FAIL for failure.
  */
     static int
-diff_write(buf_T *buf, char_u *fname)
+diff_write_buffer(buf_T *buf, diffin_T *din)
+{
+    linenr_T	lnum;
+    char_u	*s;
+    long	len = 0;
+    char_u	*ptr;
+
+    // xdiff requires one big block of memory with all the text.
+    for (lnum = 1; lnum <= buf->b_ml.ml_line_count; ++lnum)
+	len += STRLEN(ml_get_buf(buf, lnum, FALSE)) + 1;
+    ptr = lalloc(len, TRUE);
+    if (ptr == NULL)
+    {
+	// Allocating memory failed.  This can happen, because we try to read
+	// the whole buffer text into memory.  Set the failed flag, the diff
+	// will be retried with external diff.  The flag is never reset.
+	buf->b_diff_failed = TRUE;
+	if (p_verbose > 0)
+	{
+	    verbose_enter();
+	    smsg((char_u *)
+		 _("Not enough memory to use internal diff for buffer \"%s\""),
+								 buf->b_fname);
+	    verbose_leave();
+	}
+	return FAIL;
+    }
+    din->din_mmfile.ptr = (char *)ptr;
+    din->din_mmfile.size = len;
+
+    len = 0;
+    for (lnum = 1; lnum <= buf->b_ml.ml_line_count; ++lnum)
+    {
+	for (s = ml_get_buf(buf, lnum, FALSE); *s != NUL; )
+	{
+	    if (diff_flags & DIFF_ICASE)
+	    {
+		int c;
+
+		// xdiff doesn't support ignoring case, fold-case the text.
+#ifdef FEAT_MBYTE
+		int	orig_len;
+		char_u	cbuf[MB_MAXBYTES + 1];
+
+		c = PTR2CHAR(s);
+		c = enc_utf8 ? utf_fold(c) : MB_TOLOWER(c);
+		orig_len = MB_PTR2LEN(s);
+		if (mb_char2bytes(c, cbuf) != orig_len)
+		    // TODO: handle byte length difference
+		    mch_memmove(ptr + len, s, orig_len);
+		else
+		    mch_memmove(ptr + len, cbuf, orig_len);
+
+		s += orig_len;
+		len += orig_len;
+#else
+		c = *s++;
+		ptr[len++] = TOLOWER_LOC(c);
+#endif
+	    }
+	    else
+		ptr[len++] = *s++;
+	}
+	ptr[len++] = NL;
+    }
+    return OK;
+}
+
+/*
+ * Write buffer "buf" to file or memory buffer.
+ * Return FAIL for failure.
+ */
+    static int
+diff_write(buf_T *buf, diffin_T *din)
 {
     int		r;
     char_u	*save_ff;
 
+    if (din->din_fname == NULL)
+	return diff_write_buffer(buf, din);
+
+    // Always use 'fileformat' set to "unix".
     save_ff = buf->b_p_ff;
     buf->b_p_ff = vim_strsave((char_u *)FF_UNIX);
-    r = buf_write(buf, fname, NULL, (linenr_T)1, buf->b_ml.ml_line_count,
-					     NULL, FALSE, FALSE, FALSE, TRUE);
+    r = buf_write(buf, din->din_fname, NULL,
+			(linenr_T)1, buf->b_ml.ml_line_count,
+			NULL, FALSE, FALSE, FALSE, TRUE);
     free_string_option(buf->b_p_ff);
     buf->b_p_ff = save_ff;
     return r;
 }
 
 /*
+ * Update the diffs for all buffers involved.
+ */
+    static void
+diff_try_update(
+	diffio_T    *dio,
+	int	    idx_orig,
+	exarg_T	    *eap)	// "eap" can be NULL
+{
+    buf_T	*buf;
+    int		idx_new;
+
+    if (dio->dio_internal)
+    {
+	ga_init2(&dio->dio_diff.dout_ga, sizeof(char *), 1000);
+    }
+    else
+    {
+	// We need three temp file names.
+	dio->dio_orig.din_fname = vim_tempname('o', TRUE);
+	dio->dio_new.din_fname = vim_tempname('n', TRUE);
+	dio->dio_diff.dout_fname = vim_tempname('d', TRUE);
+	if (dio->dio_orig.din_fname == NULL
+		|| dio->dio_new.din_fname == NULL
+		|| dio->dio_diff.dout_fname == NULL)
+	    goto theend;
+    }
+
+    // Check external diff is actually working.
+    if (!dio->dio_internal && check_external_diff(dio) == FAIL)
+	goto theend;
+
+    // :diffupdate!
+    if (eap != NULL && eap->forceit)
+	for (idx_new = idx_orig; idx_new < DB_COUNT; ++idx_new)
+	{
+	    buf = curtab->tp_diffbuf[idx_new];
+	    if (buf_valid(buf))
+		buf_check_timestamp(buf, FALSE);
+	}
+
+    // Write the first buffer to a tempfile or mmfile_t.
+    buf = curtab->tp_diffbuf[idx_orig];
+    if (diff_write(buf, &dio->dio_orig) == FAIL)
+	goto theend;
+
+    // Make a difference between the first buffer and every other.
+    for (idx_new = idx_orig + 1; idx_new < DB_COUNT; ++idx_new)
+    {
+	buf = curtab->tp_diffbuf[idx_new];
+	if (buf == NULL || buf->b_ml.ml_mfp == NULL)
+	    continue; // skip buffer that isn't loaded
+
+	// Write the other buffer and diff with the first one.
+	if (diff_write(buf, &dio->dio_new) == FAIL)
+	    continue;
+	if (diff_file(dio) == FAIL)
+	    continue;
+
+	// Read the diff output and add each entry to the diff list.
+	diff_read(idx_orig, idx_new, &dio->dio_diff);
+
+	clear_diffin(&dio->dio_new);
+	clear_diffout(&dio->dio_diff);
+    }
+    clear_diffin(&dio->dio_orig);
+
+theend:
+    vim_free(dio->dio_orig.din_fname);
+    vim_free(dio->dio_new.din_fname);
+    vim_free(dio->dio_diff.dout_fname);
+}
+
+/*
+ * Return TRUE if the options are set to use the internal diff library.
+ * Note that if the internal diff failed for one of the buffers, the external
+ * diff will be used anyway.
+ */
+    static int
+diff_internal(void)
+{
+    return (diff_flags & DIFF_INTERNAL) != 0 && *p_dex == NUL;
+}
+
+/*
+ * Return TRUE if the internal diff failed for one of the diff buffers.
+ */
+    static int
+diff_internal_failed(void)
+{
+    int idx;
+
+    // Only need to do something when there is another buffer.
+    for (idx = 0; idx < DB_COUNT; ++idx)
+	if (curtab->tp_diffbuf[idx] != NULL
+		&& curtab->tp_diffbuf[idx]->b_diff_failed)
+	    return TRUE;
+    return FALSE;
+}
+
+/*
  * Completely update the diffs for the buffers involved.
  * This uses the ordinary "diff" command.
  * The buffers are written to a file, also for unmodified buffers (the file
  * could have been produced by autocommands, e.g. the netrw plugin).
  */
     void
-ex_diffupdate(
-    exarg_T	*eap)	    /* can be NULL */
+ex_diffupdate(exarg_T *eap)	// "eap" can be NULL
 {
-    buf_T	*buf;
     int		idx_orig;
     int		idx_new;
-    char_u	*tmp_orig;
-    char_u	*tmp_new;
-    char_u	*tmp_diff;
-    FILE	*fd;
-    int		ok;
-    int		io_error = FALSE;
+    diffio_T	diffio;
 
-    /* Delete all diffblocks. */
+    // Delete all diffblocks.
     diff_clear(curtab);
     curtab->tp_diff_invalid = FALSE;
 
-    /* Use the first buffer as the original text. */
+    // Use the first buffer as the original text.
     for (idx_orig = 0; idx_orig < DB_COUNT; ++idx_orig)
 	if (curtab->tp_diffbuf[idx_orig] != NULL)
 	    break;
     if (idx_orig == DB_COUNT)
 	return;
 
-    /* Only need to do something when there is another buffer. */
+    // Only need to do something when there is another buffer.
     for (idx_new = idx_orig + 1; idx_new < DB_COUNT; ++idx_new)
 	if (curtab->tp_diffbuf[idx_new] != NULL)
 	    break;
     if (idx_new == DB_COUNT)
 	return;
 
-    /* We need three temp file names. */
-    tmp_orig = vim_tempname('o', TRUE);
-    tmp_new = vim_tempname('n', TRUE);
-    tmp_diff = vim_tempname('d', TRUE);
-    if (tmp_orig == NULL || tmp_new == NULL || tmp_diff == NULL)
-	goto theend;
+    // Only use the internal method if it did not fail for one of the buffers.
+    vim_memset(&diffio, 0, sizeof(diffio));
+    diffio.dio_internal = diff_internal() && !diff_internal_failed();
 
-    /*
-     * Do a quick test if "diff" really works.  Otherwise it looks like there
-     * are no differences.  Can't use the return value, it's non-zero when
-     * there are differences.
-     * May try twice, first with "-a" and then without.
-     */
+    diff_try_update(&diffio, idx_orig, eap);
+    if (diffio.dio_internal && diff_internal_failed())
+    {
+	// Internal diff failed, use external diff instead.
+	vim_memset(&diffio, 0, sizeof(diffio));
+	diff_try_update(&diffio, idx_orig, eap);
+    }
+
+    // force updating cursor position on screen
+    curwin->w_valid_cursor.lnum = 0;
+
+    diff_redraw(TRUE);
+}
+
+/*
+ * Do a quick test if "diff" really works.  Otherwise it looks like there
+ * are no differences.  Can't use the return value, it's non-zero when
+ * there are differences.
+ */
+    static int
+check_external_diff(diffio_T *diffio)
+{
+    FILE	*fd;
+    int		ok;
+    int		io_error = FALSE;
+
+    // May try twice, first with "-a" and then without.
     for (;;)
     {
 	ok = FALSE;
-	fd = mch_fopen((char *)tmp_orig, "w");
+	fd = mch_fopen((char *)diffio->dio_orig.din_fname, "w");
 	if (fd == NULL)
 	    io_error = TRUE;
 	else
@@ -713,7 +954,7 @@
 	    if (fwrite("line1\n", (size_t)6, (size_t)1, fd) != 1)
 		io_error = TRUE;
 	    fclose(fd);
-	    fd = mch_fopen((char *)tmp_new, "w");
+	    fd = mch_fopen((char *)diffio->dio_new.din_fname, "w");
 	    if (fd == NULL)
 		io_error = TRUE;
 	    else
@@ -721,8 +962,9 @@
 		if (fwrite("line2\n", (size_t)6, (size_t)1, fd) != 1)
 		    io_error = TRUE;
 		fclose(fd);
-		diff_file(tmp_orig, tmp_new, tmp_diff);
-		fd = mch_fopen((char *)tmp_diff, "r");
+		fd = NULL;
+		if (diff_file(diffio) == OK)
+		    fd = mch_fopen((char *)diffio->dio_diff.dout_fname, "r");
 		if (fd == NULL)
 		    io_error = TRUE;
 		else
@@ -739,10 +981,10 @@
 		    }
 		    fclose(fd);
 		}
-		mch_remove(tmp_diff);
-		mch_remove(tmp_new);
+		mch_remove(diffio->dio_diff.dout_fname);
+		mch_remove(diffio->dio_new.din_fname);
 	    }
-	    mch_remove(tmp_orig);
+	    mch_remove(diffio->dio_orig.din_fname);
 	}
 
 #ifdef FEAT_EVAL
@@ -785,98 +1027,101 @@
 #if defined(MSWIN)
 	diff_bin_works = MAYBE;
 #endif
-	goto theend;
+	return FAIL;
     }
+    return OK;
+}
 
-    /* :diffupdate! */
-    if (eap != NULL && eap->forceit)
-	for (idx_new = idx_orig; idx_new < DB_COUNT; ++idx_new)
-	{
-	    buf = curtab->tp_diffbuf[idx_new];
-	    if (buf_valid(buf))
-		buf_check_timestamp(buf, FALSE);
-	}
+/*
+ * Invoke the xdiff function.
+ */
+    static int
+diff_file_internal(diffio_T *diffio)
+{
+    xpparam_t	    param;
+    xdemitconf_t    emit_cfg;
+    xdemitcb_t	    emit_cb;
 
-    /* Write the first buffer to a tempfile. */
-    buf = curtab->tp_diffbuf[idx_orig];
-    if (diff_write(buf, tmp_orig) == FAIL)
-	goto theend;
+    vim_memset(&param, 0, sizeof(param));
+    vim_memset(&emit_cfg, 0, sizeof(emit_cfg));
+    vim_memset(&emit_cb, 0, sizeof(emit_cb));
 
-    /* Make a difference between the first buffer and every other. */
-    for (idx_new = idx_orig + 1; idx_new < DB_COUNT; ++idx_new)
+    param.flags = diff_algorithm;
+
+    if (diff_flags & DIFF_IWHITE)
+	param.flags |= XDF_IGNORE_WHITESPACE_CHANGE;
+
+    emit_cfg.ctxlen = 0; // don't need any diff_context here
+    emit_cb.priv = &diffio->dio_diff;
+    emit_cb.outf = xdiff_out;
+    if (xdl_diff(&diffio->dio_orig.din_mmfile,
+		&diffio->dio_new.din_mmfile,
+		&param, &emit_cfg, &emit_cb) < 0)
     {
-	buf = curtab->tp_diffbuf[idx_new];
-	if (buf == NULL || buf->b_ml.ml_mfp == NULL)
-	    continue; /* skip buffer that isn't loaded */
-	if (diff_write(buf, tmp_new) == FAIL)
-	    continue;
-	diff_file(tmp_orig, tmp_new, tmp_diff);
-
-	/* Read the diff output and add each entry to the diff list. */
-	diff_read(idx_orig, idx_new, tmp_diff);
-	mch_remove(tmp_diff);
-	mch_remove(tmp_new);
+	EMSG(_("E960: Problem creating the internal diff"));
+	return FAIL;
     }
-    mch_remove(tmp_orig);
-
-    /* force updating cursor position on screen */
-    curwin->w_valid_cursor.lnum = 0;
-
-    diff_redraw(TRUE);
-
-theend:
-    vim_free(tmp_orig);
-    vim_free(tmp_new);
-    vim_free(tmp_diff);
+    return OK;
 }
 
 /*
  * Make a diff between files "tmp_orig" and "tmp_new", results in "tmp_diff".
+ * return OK or FAIL;
  */
-    static void
-diff_file(
-    char_u	*tmp_orig,
-    char_u	*tmp_new,
-    char_u	*tmp_diff)
+    static int
+diff_file(diffio_T *dio)
 {
     char_u	*cmd;
     size_t	len;
+    char_u	*tmp_orig = dio->dio_orig.din_fname;
+    char_u	*tmp_new = dio->dio_new.din_fname;
+    char_u	*tmp_diff = dio->dio_diff.dout_fname;
 
 #ifdef FEAT_EVAL
     if (*p_dex != NUL)
-	/* Use 'diffexpr' to generate the diff file. */
+    {
+	// Use 'diffexpr' to generate the diff file.
 	eval_diff(tmp_orig, tmp_new, tmp_diff);
+	return OK;
+    }
     else
 #endif
+    // Use xdiff for generating the diff.
+    if (dio->dio_internal)
+    {
+	return diff_file_internal(dio);
+    }
+    else
     {
 	len = STRLEN(tmp_orig) + STRLEN(tmp_new)
 				      + STRLEN(tmp_diff) + STRLEN(p_srr) + 27;
 	cmd = alloc((unsigned)len);
-	if (cmd != NULL)
-	{
-	    /* We don't want $DIFF_OPTIONS to get in the way. */
-	    if (getenv("DIFF_OPTIONS"))
-		vim_setenv((char_u *)"DIFF_OPTIONS", (char_u *)"");
+	if (cmd == NULL)
+	    return FAIL;
 
-	    /* Build the diff command and execute it.  Always use -a, binary
-	     * differences are of no use.  Ignore errors, diff returns
-	     * non-zero when differences have been found. */
-	    vim_snprintf((char *)cmd, len, "diff %s%s%s%s%s %s",
-		    diff_a_works == FALSE ? "" : "-a ",
+	// We don't want $DIFF_OPTIONS to get in the way.
+	if (getenv("DIFF_OPTIONS"))
+	    vim_setenv((char_u *)"DIFF_OPTIONS", (char_u *)"");
+
+	// Build the diff command and execute it.  Always use -a, binary
+	// differences are of no use.  Ignore errors, diff returns
+	// non-zero when differences have been found.
+	vim_snprintf((char *)cmd, len, "diff %s%s%s%s%s %s",
+		diff_a_works == FALSE ? "" : "-a ",
 #if defined(MSWIN)
-		    diff_bin_works == TRUE ? "--binary " : "",
+		diff_bin_works == TRUE ? "--binary " : "",
 #else
-		    "",
+		"",
 #endif
-		    (diff_flags & DIFF_IWHITE) ? "-b " : "",
-		    (diff_flags & DIFF_ICASE) ? "-i " : "",
-		    tmp_orig, tmp_new);
-	    append_redir(cmd, (int)len, p_srr, tmp_diff);
-	    block_autocmds();	/* Avoid ShellCmdPost stuff */
-	    (void)call_shell(cmd, SHELL_FILTER|SHELL_SILENT|SHELL_DOOUT);
-	    unblock_autocmds();
-	    vim_free(cmd);
-	}
+		(diff_flags & DIFF_IWHITE) ? "-b " : "",
+		(diff_flags & DIFF_ICASE) ? "-i " : "",
+		tmp_orig, tmp_new);
+	append_redir(cmd, (int)len, p_srr, tmp_diff);
+	block_autocmds();	// avoid ShellCmdPost stuff
+	(void)call_shell(cmd, SHELL_FILTER|SHELL_SILENT|SHELL_DOOUT);
+	unblock_autocmds();
+	vim_free(cmd);
+	return OK;
     }
 }
 
@@ -1282,89 +1527,105 @@
  */
     static void
 diff_read(
-    int		idx_orig,	/* idx of original file */
-    int		idx_new,	/* idx of new file */
-    char_u	*fname)		/* name of diff output file */
+    int		idx_orig,	// idx of original file
+    int		idx_new,	// idx of new file
+    diffout_T	*dout)		// diff output
 {
-    FILE	*fd;
+    FILE	*fd = NULL;
+    int		line_idx = 0;
     diff_T	*dprev = NULL;
     diff_T	*dp = curtab->tp_first_diff;
     diff_T	*dn, *dpl;
-    long	f1, l1, f2, l2;
     char_u	linebuf[LBUFLEN];   /* only need to hold the diff line */
-    int		difftype;
-    char_u	*p;
+    char_u	*line;
     long	off;
     int		i;
     linenr_T	lnum_orig, lnum_new;
     long	count_orig, count_new;
     int		notset = TRUE;	    /* block "*dp" not set yet */
+    enum {
+	DIFF_ED,
+	DIFF_UNIFIED,
+	DIFF_NONE
+    } diffstyle = DIFF_NONE;
 
-    fd = mch_fopen((char *)fname, "r");
-    if (fd == NULL)
+    if (dout->dout_fname == NULL)
     {
-	EMSG(_("E98: Cannot read diff output"));
-	return;
+	diffstyle = DIFF_UNIFIED;
+    }
+    else
+    {
+	fd = mch_fopen((char *)dout->dout_fname, "r");
+	if (fd == NULL)
+	{
+	    EMSG(_("E98: Cannot read diff output"));
+	    return;
+	}
     }
 
     for (;;)
     {
-	if (tag_fgets(linebuf, LBUFLEN, fd))
-	    break;		/* end of file */
-	if (!isdigit(*linebuf))
-	    continue;		/* not the start of a diff block */
-
-	/* This line must be one of three formats:
-	 * {first}[,{last}]c{first}[,{last}]
-	 * {first}a{first}[,{last}]
-	 * {first}[,{last}]d{first}
-	 */
-	p = linebuf;
-	f1 = getdigits(&p);
-	if (*p == ',')
+	if (fd == NULL)
 	{
-	    ++p;
-	    l1 = getdigits(&p);
-	}
-	else
-	    l1 = f1;
-	if (*p != 'a' && *p != 'c' && *p != 'd')
-	    continue;		/* invalid diff format */
-	difftype = *p++;
-	f2 = getdigits(&p);
-	if (*p == ',')
-	{
-	    ++p;
-	    l2 = getdigits(&p);
-	}
-	else
-	    l2 = f2;
-	if (l1 < f1 || l2 < f2)
-	    continue;		/* invalid line range */
-
-	if (difftype == 'a')
-	{
-	    lnum_orig = f1 + 1;
-	    count_orig = 0;
+	    if (line_idx >= dout->dout_ga.ga_len)
+		break;	    // did last line
+	    line = ((char_u **)dout->dout_ga.ga_data)[line_idx++];
 	}
 	else
 	{
-	    lnum_orig = f1;
-	    count_orig = l1 - f1 + 1;
-	}
-	if (difftype == 'd')
-	{
-	    lnum_new = f2 + 1;
-	    count_new = 0;
-	}
-	else
-	{
-	    lnum_new = f2;
-	    count_new = l2 - f2 + 1;
+	    if (tag_fgets(linebuf, LBUFLEN, fd))
+		break;		// end of file
+	    line = linebuf;
 	}
 
-	/* Go over blocks before the change, for which orig and new are equal.
-	 * Copy blocks from orig to new. */
+	if (diffstyle == DIFF_NONE)
+	{
+	    // Determine diff style.
+	    // ed like diff looks like this:
+	    // {first}[,{last}]c{first}[,{last}]
+	    // {first}a{first}[,{last}]
+	    // {first}[,{last}]d{first}
+	    //
+	    // unified diff looks like this:
+	    // --- file1       2018-03-20 13:23:35.783153140 +0100
+	    // +++ file2       2018-03-20 13:23:41.183156066 +0100
+	    // @@ -1,3 +1,5 @@
+	    if (isdigit(*line))
+		diffstyle = DIFF_ED;
+	    else if ((STRNCMP(line, "@@ ", 3) == 0))
+	       diffstyle = DIFF_UNIFIED;
+	    else if ((STRNCMP(line, "--- ", 4) == 0)
+		    && (tag_fgets(linebuf, LBUFLEN, fd) == 0)
+		    && (STRNCMP(line, "+++ ", 4) == 0)
+		    && (tag_fgets(linebuf, LBUFLEN, fd) == 0)
+		    && (STRNCMP(line, "@@ ", 3) == 0))
+		diffstyle = DIFF_UNIFIED;
+	}
+
+	if (diffstyle == DIFF_ED)
+	{
+	    if (!isdigit(*line))
+		continue;	// not the start of a diff block
+	    if (parse_diff_ed(line, &lnum_orig, &count_orig,
+						&lnum_new, &count_new) == FAIL)
+		continue;
+	}
+	else if (diffstyle == DIFF_UNIFIED)
+	{
+	    if (STRNCMP(line, "@@ ", 3)  != 0)
+		continue;	// not the start of a diff block
+	    if (parse_diff_unified(line, &lnum_orig, &count_orig,
+						&lnum_new, &count_new) == FAIL)
+		continue;
+	}
+	else
+	{
+	    EMSG(_("E959: Invalid diff format."));
+	    break;
+	}
+
+	// Go over blocks before the change, for which orig and new are equal.
+	// Copy blocks from orig to new.
 	while (dp != NULL
 		&& lnum_orig > dp->df_lnum[idx_orig] + dp->df_count[idx_orig])
 	{
@@ -1379,14 +1640,14 @@
 		&& lnum_orig <= dp->df_lnum[idx_orig] + dp->df_count[idx_orig]
 		&& lnum_orig + count_orig >= dp->df_lnum[idx_orig])
 	{
-	    /* New block overlaps with existing block(s).
-	     * First find last block that overlaps. */
+	    // New block overlaps with existing block(s).
+	    // First find last block that overlaps.
 	    for (dpl = dp; dpl->df_next != NULL; dpl = dpl->df_next)
 		if (lnum_orig + count_orig < dpl->df_next->df_lnum[idx_orig])
 		    break;
 
-	    /* If the newly found block starts before the old one, set the
-	     * start back a number of lines. */
+	    // If the newly found block starts before the old one, set the
+	    // start back a number of lines.
 	    off = dp->df_lnum[idx_orig] - lnum_orig;
 	    if (off > 0)
 	    {
@@ -1398,24 +1659,24 @@
 	    }
 	    else if (notset)
 	    {
-		/* new block inside existing one, adjust new block */
+		// new block inside existing one, adjust new block
 		dp->df_lnum[idx_new] = lnum_new + off;
 		dp->df_count[idx_new] = count_new - off;
 	    }
 	    else
-		/* second overlap of new block with existing block */
+		// second overlap of new block with existing block
 		dp->df_count[idx_new] += count_new - count_orig
 		    + dpl->df_lnum[idx_orig] + dpl->df_count[idx_orig]
 		    - (dp->df_lnum[idx_orig] + dp->df_count[idx_orig]);
 
-	    /* Adjust the size of the block to include all the lines to the
-	     * end of the existing block or the new diff, whatever ends last. */
+	    // Adjust the size of the block to include all the lines to the
+	    // end of the existing block or the new diff, whatever ends last.
 	    off = (lnum_orig + count_orig)
 			 - (dpl->df_lnum[idx_orig] + dpl->df_count[idx_orig]);
 	    if (off < 0)
 	    {
-		/* new change ends in existing block, adjust the end if not
-		 * done already */
+		// new change ends in existing block, adjust the end if not
+		// done already
 		if (notset)
 		    dp->df_count[idx_new] += -off;
 		off = 0;
@@ -1425,7 +1686,7 @@
 		    dp->df_count[i] = dpl->df_lnum[i] + dpl->df_count[i]
 						       - dp->df_lnum[i] + off;
 
-	    /* Delete the diff blocks that have been merged into one. */
+	    // Delete the diff blocks that have been merged into one.
 	    dn = dp->df_next;
 	    dp->df_next = dpl->df_next;
 	    while (dn != dp->df_next)
@@ -1437,7 +1698,7 @@
 	}
 	else
 	{
-	    /* Allocate a new diffblock. */
+	    // Allocate a new diffblock.
 	    dp = diff_alloc_new(curtab, dprev, dp);
 	    if (dp == NULL)
 		goto done;
@@ -1447,17 +1708,17 @@
 	    dp->df_lnum[idx_new] = lnum_new;
 	    dp->df_count[idx_new] = count_new;
 
-	    /* Set values for other buffers, these must be equal to the
-	     * original buffer, otherwise there would have been a change
-	     * already. */
+	    // Set values for other buffers, these must be equal to the
+	    // original buffer, otherwise there would have been a change
+	    // already.
 	    for (i = idx_orig + 1; i < idx_new; ++i)
 		if (curtab->tp_diffbuf[i] != NULL)
 		    diff_copy_entry(dprev, dp, idx_orig, i);
 	}
-	notset = FALSE;		/* "*dp" has been set */
+	notset = FALSE;		// "*dp" has been set
     }
 
-    /* for remaining diff blocks orig and new are equal */
+    // for remaining diff blocks orig and new are equal
     while (dp != NULL)
     {
 	if (notset)
@@ -1468,7 +1729,8 @@
     }
 
 done:
-    fclose(fd);
+    if (fd != NULL)
+	fclose(fd);
 }
 
 /*
@@ -1860,6 +2122,7 @@
     int		diff_context_new = 6;
     int		diff_flags_new = 0;
     int		diff_foldcolumn_new = 2;
+    long	diff_algorithm_new = 0;
     tabpage_T	*tp;
 
     p = p_dip;
@@ -1905,6 +2168,41 @@
 	    p += 9;
 	    diff_flags_new |= DIFF_HIDDEN_OFF;
 	}
+	else if (STRNCMP(p, "indent-heuristic", 16) == 0)
+	{
+	    p += 16;
+	    diff_algorithm_new |= XDF_INDENT_HEURISTIC;
+	}
+	else if (STRNCMP(p, "internal", 8) == 0)
+	{
+	    p += 8;
+	    diff_flags_new |= DIFF_INTERNAL;
+	}
+	else if (STRNCMP(p, "algorithm:", 10) == 0)
+	{
+	    p += 10;
+	    if (STRNCMP(p, "myers", 5) == 0)
+	    {
+		p += 5;
+		diff_algorithm_new = 0;
+	    }
+	    else if (STRNCMP(p, "minimal", 7) == 0)
+	    {
+		p += 7;
+		diff_algorithm_new = XDF_NEED_MINIMAL;
+	    }
+	    else if (STRNCMP(p, "patience", 8) == 0)
+	    {
+		p += 8;
+		diff_algorithm_new = XDF_PATIENCE_DIFF;
+	    }
+	    else if (STRNCMP(p, "histogram", 9) == 0)
+	    {
+		p += 9;
+		diff_algorithm_new = XDF_HISTOGRAM_DIFF;
+	    }
+	}
+
 	if (*p != ',' && *p != NUL)
 	    return FAIL;
 	if (*p == ',')
@@ -1916,13 +2214,14 @@
 	return FAIL;
 
     /* If "icase" or "iwhite" was added or removed, need to update the diff. */
-    if (diff_flags != diff_flags_new)
+    if (diff_flags != diff_flags_new || diff_algorithm != diff_algorithm_new)
 	FOR_ALL_TABPAGES(tp)
 	    tp->tp_diff_invalid = TRUE;
 
     diff_flags = diff_flags_new;
     diff_context = diff_context_new;
     diff_foldcolumn = diff_foldcolumn_new;
+    diff_algorithm = diff_algorithm_new;
 
     diff_redraw(TRUE);
 
@@ -2690,4 +2989,156 @@
     return n;
 }
 
+/*
+ * Handle an ED style diff line.
+ * Return FAIL if the line does not contain diff info.
+ */
+    static int
+parse_diff_ed(
+	char_u	    *line,
+	linenr_T    *lnum_orig,
+	long	    *count_orig,
+	linenr_T    *lnum_new,
+	long	    *count_new)
+{
+    char_u *p;
+    long    f1, l1, f2, l2;
+    int	    difftype;
+
+    // The line must be one of three formats:
+    // change: {first}[,{last}]c{first}[,{last}]
+    // append: {first}a{first}[,{last}]
+    // delete: {first}[,{last}]d{first}
+    p = line;
+    f1 = getdigits(&p);
+    if (*p == ',')
+    {
+	++p;
+	l1 = getdigits(&p);
+    }
+    else
+	l1 = f1;
+    if (*p != 'a' && *p != 'c' && *p != 'd')
+	return FAIL;		// invalid diff format
+    difftype = *p++;
+    f2 = getdigits(&p);
+    if (*p == ',')
+    {
+	++p;
+	l2 = getdigits(&p);
+    }
+    else
+	l2 = f2;
+    if (l1 < f1 || l2 < f2)
+	return FAIL;
+
+    if (difftype == 'a')
+    {
+	*lnum_orig = f1 + 1;
+	*count_orig = 0;
+    }
+    else
+    {
+	*lnum_orig = f1;
+	*count_orig = l1 - f1 + 1;
+    }
+    if (difftype == 'd')
+    {
+	*lnum_new = f2 + 1;
+	*count_new = 0;
+    }
+    else
+    {
+	*lnum_new = f2;
+	*count_new = l2 - f2 + 1;
+    }
+    return OK;
+}
+
+/*
+ * Parses unified diff with zero(!) context lines.
+ * Return FAIL if there is no diff information in "line".
+ */
+    static int
+parse_diff_unified(
+	char_u	    *line,
+	linenr_T    *lnum_orig,
+	long	    *count_orig,
+	linenr_T    *lnum_new,
+	long	    *count_new)
+{
+    char_u *p;
+    long    oldline, oldcount, newline, newcount;
+
+    // Parse unified diff hunk header:
+    // @@ -oldline,oldcount +newline,newcount @@
+    p = line;
+    if (*p++ == '@' && *p++ == '@' && *p++ == ' ' && *p++ == '-')
+    {
+	oldline = getdigits(&p);
+	if (*p == ',')
+	{
+	    ++p;
+	    oldcount = getdigits(&p);
+	}
+	else
+	    oldcount = 1;
+	if (*p++ == ' ' && *p++ == '+')
+	{
+	    newline = getdigits(&p);
+	    if (*p == ',')
+	    {
+		++p;
+		newcount = getdigits(&p);
+	    }
+	    else
+		newcount = 1;
+	}
+	else
+	    return FAIL;	// invalid diff format
+
+	if (oldcount == 0)
+	    oldline += 1;
+	if (newcount == 0)
+	    newline += 1;
+	if (newline == 0)
+	    newline = 1;
+
+	*lnum_orig = oldline;
+	*count_orig = oldcount;
+	*lnum_new = newline;
+	*count_new = newcount;
+
+	return OK;
+    }
+
+    return FAIL;
+}
+
+/*
+ * Callback function for the xdl_diff() function.
+ * Stores the diff output in a grow array.
+ */
+    static int
+xdiff_out(void *priv, mmbuffer_t *mb, int nbuf)
+{
+    diffout_T	*dout = (diffout_T *)priv;
+    int		i;
+    char_u	*p;
+
+    for (i = 0; i < nbuf; i++)
+    {
+	// We are only interested in the header lines, skip text lines.
+	if (STRNCMP(mb[i].ptr, "@@ ", 3)  != 0)
+	    continue;
+	if (ga_grow(&dout->dout_ga, 1) == FAIL)
+	    return -1;
+	p = vim_strnsave((char_u *)mb[i].ptr, mb[i].size);
+	if (p == NULL)
+	    return -1;
+	((char_u **)dout->dout_ga.ga_data)[dout->dout_ga.ga_len++] = p;
+    }
+    return 0;
+}
+
 #endif	/* FEAT_DIFF */
diff --git a/src/structs.h b/src/structs.h
index 253f774..ee56bd3 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -2433,7 +2433,9 @@
     term_T	*b_term;	/* When not NULL this buffer is for a terminal
 				 * window. */
 #endif
-
+#ifdef FEAT_DIFF
+    int		b_diff_failed;	// internal diff failed for this buffer
+#endif
 }; /* file_buffer */
 
 
diff --git a/src/testdir/dumps/Test_diff_01.dump b/src/testdir/dumps/Test_diff_01.dump
new file mode 100644
index 0000000..0dbce1f
--- /dev/null
+++ b/src/testdir/dumps/Test_diff_01.dump
@@ -0,0 +1,20 @@
+| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@34||+1#0000000#ffffff0| +0#0000e05#a8a8a8255@1|0+0#0000000#5fd7ff255| @33
+| +0#0000e05#a8a8a8255@1|1+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|1+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|2+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|2+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|3+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|3+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|4+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|4+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|5+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|5+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|6+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|6+0#0000000#ffffff0| @33
+|++0#0000e05#a8a8a8255| |+|-@1| @1|4| |l|i|n|e|s|:| |7|-@19||+1#0000000#ffffff0|++0#0000e05#a8a8a8255| |+|-@1| @1|4| |l|i|n|e|s|:| |7|-@19
+| @1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+|X+3#0000000&|f|i|l|e|1| @12|1|,|1| @11|A|l@1| |X+1&&|f|i|l|e|2| @12|1|,|1| @11|A|l@1
+|:+0&&> @73
diff --git a/src/testdir/dumps/Test_diff_02.dump b/src/testdir/dumps/Test_diff_02.dump
new file mode 100644
index 0000000..78f7978
--- /dev/null
+++ b/src/testdir/dumps/Test_diff_02.dump
@@ -0,0 +1,20 @@
+| +0#0000e05#a8a8a8255@1|0+0#0000000#5fd7ff255| @33||+1&#ffffff0| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@34
+| +0#0000e05#a8a8a8255@1|1+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|1+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|2+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|2+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|3+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|3+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|4+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|4+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|5+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|5+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|6+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|6+0#0000000#ffffff0| @33
+|++0#0000e05#a8a8a8255| |+|-@1| @1|4| |l|i|n|e|s|:| |7|-@19||+1#0000000#ffffff0|++0#0000e05#a8a8a8255| |+|-@1| @1|4| |l|i|n|e|s|:| |7|-@19
+| @1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+|X+3#0000000&|f|i|l|e|1| @12|1|,|1| @11|A|l@1| |X+1&&|f|i|l|e|2| @12|1|,|1| @11|A|l@1
+|:+0&&> @73
diff --git a/src/testdir/dumps/Test_diff_03.dump b/src/testdir/dumps/Test_diff_03.dump
new file mode 100644
index 0000000..60916a8
--- /dev/null
+++ b/src/testdir/dumps/Test_diff_03.dump
@@ -0,0 +1,20 @@
+|++0#0000e05#a8a8a8255| |+|-@1| @1|4| |l|i|n|e|s|:| |1|-@19||+1#0000000#ffffff0|++0#0000e05#a8a8a8255| |+|-@1| @1|4| |l|i|n|e|s|:| |1|-@19
+| @1|5+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|5+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|6+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|6+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|7+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|7+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|8+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|8+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|9+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|9+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|1+0#0000000#ffffff0|0| @32||+1&&| +0#0000e05#a8a8a8255@1|1+0#0000000#ffffff0|0| @32
+| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@34||+1#0000000#ffffff0| +0#0000e05#a8a8a8255@1|1+0#0000000#5fd7ff255@1| @32
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+|X+3#0000000&|f|i|l|e|1| @12|1|,|1| @11|A|l@1| |X+1&&|f|i|l|e|2| @12|1|,|1| @11|A|l@1
+|:+0&&> @73
diff --git a/src/testdir/dumps/Test_diff_04.dump b/src/testdir/dumps/Test_diff_04.dump
new file mode 100644
index 0000000..ba9cdd8
--- /dev/null
+++ b/src/testdir/dumps/Test_diff_04.dump
@@ -0,0 +1,20 @@
+|++0#0000e05#a8a8a8255| |+|-@1| @1|4| |l|i|n|e|s|:| |1|-@19||+1#0000000#ffffff0|++0#0000e05#a8a8a8255| |+|-@1| @1|4| |l|i|n|e|s|:| |1|-@19
+| @1|5+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|5+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|6+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|6+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|7+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|7+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|8+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|8+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|9+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|9+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|1+0#0000000#ffffff0|0| @32||+1&&| +0#0000e05#a8a8a8255@1|1+0#0000000#ffffff0|0| @32
+| +0#0000e05#a8a8a8255@1|1+0#0000000#5fd7ff255@1| @32||+1&#ffffff0| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@34
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
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+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
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diff --git a/src/testdir/dumps/Test_diff_05.dump b/src/testdir/dumps/Test_diff_05.dump
new file mode 100644
index 0000000..7a5d540
--- /dev/null
+++ b/src/testdir/dumps/Test_diff_05.dump
@@ -0,0 +1,20 @@
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diff --git a/src/testdir/dumps/Test_diff_06.dump b/src/testdir/dumps/Test_diff_06.dump
new file mode 100644
index 0000000..8cd68fd
--- /dev/null
+++ b/src/testdir/dumps/Test_diff_06.dump
@@ -0,0 +1,20 @@
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diff --git a/src/testdir/dumps/Test_diff_07.dump b/src/testdir/dumps/Test_diff_07.dump
new file mode 100644
index 0000000..97864c6
--- /dev/null
+++ b/src/testdir/dumps/Test_diff_07.dump
@@ -0,0 +1,20 @@
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diff --git a/src/testdir/dumps/Test_diff_08.dump b/src/testdir/dumps/Test_diff_08.dump
new file mode 100644
index 0000000..6445a57
--- /dev/null
+++ b/src/testdir/dumps/Test_diff_08.dump
@@ -0,0 +1,20 @@
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diff --git a/src/testdir/dumps/Test_diff_09.dump b/src/testdir/dumps/Test_diff_09.dump
new file mode 100644
index 0000000..6445a57
--- /dev/null
+++ b/src/testdir/dumps/Test_diff_09.dump
@@ -0,0 +1,20 @@
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new file mode 100644
index 0000000..70b9c82
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new file mode 100644
index 0000000..0e4268e
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new file mode 100644
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new file mode 100644
index 0000000..cc1f1ad
--- /dev/null
+++ b/src/testdir/dumps/Test_diff_13.dump
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new file mode 100644
index 0000000..5f9b75f
--- /dev/null
+++ b/src/testdir/dumps/Test_diff_14.dump
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+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+|X+3#0000000&|f|i|l|e|1| @12|1|,|1| @11|A|l@1| |X+1&&|f|i|l|e|2| @12|1|,|1| @11|A|l@1
+|:+0&&> @73
diff --git a/src/testdir/dumps/Test_diff_15.dump b/src/testdir/dumps/Test_diff_15.dump
new file mode 100644
index 0000000..0eb1813
--- /dev/null
+++ b/src/testdir/dumps/Test_diff_15.dump
@@ -0,0 +1,20 @@
+| +0#0000e05#a8a8a8255@1>i+0#0000000#ffffff0|n|t| |m|a|i|n|(|)| @24||+1&&| +0#0000e05#a8a8a8255@1|i+0#0000000#ffffff0|n|t| |m|a|i|n|(|)| @24
+| +0#0000e05#a8a8a8255@1|{+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|{+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@34||+1#0000000#ffffff0| +0#0000e05#a8a8a8255@1| +0#0000000#5fd7ff255@2|i|f| |(|0|)| @25
+| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@34||+1#0000000#ffffff0| +0#0000e05#a8a8a8255@1| +0#0000000#5fd7ff255@2|{| @30
+| +0#0000e05#a8a8a8255@1| +0#0000000#ffffff0@2|p|r|i|n|t|f|(|"|H|e|l@1|o|,| |W|o|r|l|d|!|"|)|;| @7||+1&&| +0#0000e05#a8a8a8255@1| +0#0000000#ffffff0@5|p|r|i|n|t|f|(|"|H|e|l@1|o|,| |W|o|r|l|d|!|"|)|;| @4
+| +0#0000e05#a8a8a8255@1| +0#0000000#ffffff0@2|r|e|t|u|r|n| |0|;| @22||+1&&| +0#0000e05#a8a8a8255@1| +0#0000000#ffffff0@5|r|e|t|u|r|n| |0|;| @19
+| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@34||+1#0000000#ffffff0| +0#0000e05#a8a8a8255@1| +0#0000000#5fd7ff255@2|}| @30
+| +0#0000e05#a8a8a8255@1|}+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|}+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+|X+3#0000000&|f|i|l|e|1| @12|1|,|1| @11|A|l@1| |X+1&&|f|i|l|e|2| @12|1|,|1| @11|A|l@1
+|:+0&&|s|e|t| |d|i|f@1|o|p|t|&|v|i|m| |d|i|f@1|o|p|t|+|=|f|i|l@1|e|r| |d|i|f@1|o|p|t|+|=|i|w|h|i|t|e| @26
diff --git a/src/testdir/dumps/Test_diff_16.dump b/src/testdir/dumps/Test_diff_16.dump
new file mode 100644
index 0000000..74ad5b6
--- /dev/null
+++ b/src/testdir/dumps/Test_diff_16.dump
@@ -0,0 +1,20 @@
+| +0#0000e05#a8a8a8255@1>i+0#0000000#ffffff0|n|t| |m|a|i|n|(|)| @24||+1&&| +0#0000e05#a8a8a8255@1|i+0#0000000#ffffff0|n|t| |m|a|i|n|(|)| @24
+| +0#0000e05#a8a8a8255@1|{+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|{+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@34||+1#0000000#ffffff0| +0#0000e05#a8a8a8255@1| +0#0000000#5fd7ff255@2|i|f| |(|0|)| @25
+| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@34||+1#0000000#ffffff0| +0#0000e05#a8a8a8255@1| +0#0000000#5fd7ff255@2|{| @30
+| +0#0000e05#a8a8a8255@1| +0#0000000#ffffff0@2|p|r|i|n|t|f|(|"|H|e|l@1|o|,| |W|o|r|l|d|!|"|)|;| @7||+1&&| +0#0000e05#a8a8a8255@1| +0#0000000#ffffff0@5|p|r|i|n|t|f|(|"|H|e|l@1|o|,| |W|o|r|l|d|!|"|)|;| @4
+| +0#0000e05#a8a8a8255@1| +0#0000000#ffffff0@2|r|e|t|u|r|n| |0|;| @22||+1&&| +0#0000e05#a8a8a8255@1| +0#0000000#ffffff0@5|r|e|t|u|r|n| |0|;| @19
+| +0#0000e05#a8a8a8255@1|-+0#4040ff13#afffff255@34||+1#0000000#ffffff0| +0#0000e05#a8a8a8255@1| +0#0000000#5fd7ff255@2|}| @30
+| +0#0000e05#a8a8a8255@1|}+0#0000000#ffffff0| @33||+1&&| +0#0000e05#a8a8a8255@1|}+0#0000000#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33||+1#0000000&| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @33
+|X+3#0000000&|f|i|l|e|1| @12|1|,|1| @11|A|l@1| |X+1&&|f|i|l|e|2| @12|1|,|1| @11|A|l@1
+|:+0&&|s|e|t| |d|i|f@1|o|p|t|+|=|i|n|t|e|r|n|a|l| @52
diff --git a/src/testdir/test_diffmode.vim b/src/testdir/test_diffmode.vim
index d6c5c83..c3c1eaf 100644
--- a/src/testdir/test_diffmode.vim
+++ b/src/testdir/test_diffmode.vim
@@ -1,4 +1,6 @@
 " Tests for diff mode
+source shared.vim
+source screendump.vim
 
 func Test_diff_fold_sync()
   enew!
@@ -33,6 +35,18 @@
 endfunc
 
 func Test_vert_split()
+  set diffopt=filler
+  call Common_vert_split()
+  set diffopt&
+endfunc
+
+func Test_vert_split_internal()
+  set diffopt=internal,filler
+  call Common_vert_split()
+  set diffopt&
+endfunc
+
+func Common_vert_split()
   " Disable the title to avoid xterm keeping the wrong one.
   set notitle noicon
   new
@@ -275,10 +289,8 @@
   bwipe!
 endfunc
 
-func Test_diffopt_icase()
-  set diffopt=icase,foldcolumn:0
-
-  e one
+func Common_icase_test()
+  edit one
   call setline(1, ['One', 'Two', 'Three', 'Four', 'Fi#ve'])
   redraw
   let normattr = screenattr(1, 1)
@@ -300,32 +312,54 @@
 
   diffoff!
   %bwipe!
+endfunc
+
+func Test_diffopt_icase()
+  set diffopt=icase,foldcolumn:0
+  call Common_icase_test()
   set diffopt&
 endfunc
 
-func Test_diffopt_iwhite()
-  set diffopt=iwhite,foldcolumn:0
+func Test_diffopt_icase_internal()
+  set diffopt=icase,foldcolumn:0,internal
+  call Common_icase_test()
+  set diffopt&
+endfunc
 
-  e one
-  " Difference in trailing spaces should be ignored,
+func Common_iwhite_test()
+  edit one
+  " Difference in trailing spaces and amount of spaces should be ignored,
   " but not other space differences.
-  call setline(1, ["One \t", 'Two', 'Three', 'Four'])
+  call setline(1, ["One \t", 'Two', 'Three', 'one two', 'one two', 'Four'])
   redraw
   let normattr = screenattr(1, 1)
   diffthis
 
   botright vert new two
-  call setline(1, ["One\t ", "Two\t ", 'Three', ' Four'])
+  call setline(1, ["One\t ", "Two\t ", 'Three', 'one   two', 'onetwo', ' Four'])
   diffthis
 
   redraw
   call assert_equal(normattr, screenattr(1, 1))
   call assert_equal(normattr, screenattr(2, 1))
   call assert_equal(normattr, screenattr(3, 1))
-  call assert_notequal(normattr, screenattr(4, 1))
+  call assert_equal(normattr, screenattr(4, 1))
+  call assert_notequal(normattr, screenattr(5, 1))
+  call assert_notequal(normattr, screenattr(6, 1))
 
   diffoff!
   %bwipe!
+endfunc
+
+func Test_diffopt_iwhite()
+  set diffopt=iwhite,foldcolumn:0
+  call Common_iwhite_test()
+  set diffopt&
+endfunc
+
+func Test_diffopt_iwhite_internal()
+  set diffopt=internal,iwhite,foldcolumn:0
+  call Common_iwhite_test()
   set diffopt&
 endfunc
 
@@ -339,8 +373,13 @@
 
   set diffopt=context:2
   call assert_equal('+--  2 lines: 1', foldtextresult(1))
+  set diffopt=internal,context:2
+  call assert_equal('+--  2 lines: 1', foldtextresult(1))
+
   set diffopt=context:1
   call assert_equal('+--  3 lines: 1', foldtextresult(1))
+  set diffopt=internal,context:1
+  call assert_equal('+--  3 lines: 1', foldtextresult(1))
 
   diffoff!
   %bwipe!
@@ -348,7 +387,7 @@
 endfunc
 
 func Test_diffopt_horizontal()
-  set diffopt=horizontal
+  set diffopt=internal,horizontal
   diffsplit
 
   call assert_equal(&columns, winwidth(1))
@@ -362,7 +401,7 @@
 endfunc
 
 func Test_diffopt_vertical()
-  set diffopt=vertical
+  set diffopt=internal,vertical
   diffsplit
 
   call assert_equal(&lines - 2, winheight(1))
@@ -376,7 +415,7 @@
 endfunc
 
 func Test_diffopt_hiddenoff()
-  set diffopt=filler,foldcolumn:0,hiddenoff
+  set diffopt=internal,filler,foldcolumn:0,hiddenoff
   e! one
   call setline(1, ['Two', 'Three'])
   redraw
@@ -399,7 +438,7 @@
 endfunc
 
 func Test_diffoff_hidden()
-  set diffopt=filler,foldcolumn:0
+  set diffopt=internal,filler,foldcolumn:0
   e! one
   call setline(1, ['Two', 'Three'])
   redraw
@@ -629,3 +668,118 @@
   bwipe!
   bwipe!
 endfunc
+
+func WriteDiffFiles(list1, list2)
+  call writefile(a:list1, 'Xfile1')
+  call writefile(a:list2, 'Xfile2')
+endfunc
+
+" Verify a screendump with both the external and external diff.
+func VerifyBoth(buf, dumpfile, extra)
+  call term_sendkeys(a:buf, ":diffupdate!\<cr>")
+  " trailing : for leaving the cursor on the command line
+  for cmd in [":set diffopt=filler" . a:extra . "\<cr>:", ":set diffopt+=internal\<cr>:"]
+    call term_sendkeys(a:buf, cmd)
+    if VerifyScreenDump(a:buf, a:dumpfile, {}, cmd =~ 'internal' ? 'internal' : 'external')
+      break " don't let the next iteration overwrite the "failed" file.
+    endif
+  endfor
+endfunc
+
+func Test_diff_screen()
+  if !CanRunVimInTerminal() || !has('menu')
+    return
+  endif
+  " clean up already existing swap files, just in case
+  call delete('.Xfile1.swp')
+  call delete('.Xfile2.swp')
+
+  " Test 1: Add a line in beginning of file 2
+  call WriteDiffFiles([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
+  let buf = RunVimInTerminal('-d Xfile1 Xfile2', {})
+  " Set autoread mode, ,so that Vim won't complain once we re-write the test
+  " files
+  call term_sendkeys(buf, ":set autoread\<cr>\<c-w>w:set autoread\<cr>\<c-w>w")
+
+  call VerifyBoth(buf, 'Test_diff_01', '')
+
+  " Test 2: Add a line in beginning of file 1
+  call WriteDiffFiles([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10], [1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
+  call VerifyBoth(buf, 'Test_diff_02', '')
+
+  " Test 3: Add a line at the end of file 2
+  call WriteDiffFiles([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11])
+  call VerifyBoth(buf, 'Test_diff_03', '')
+
+  " Test 4: Add a line at the end of file 1
+  call WriteDiffFiles([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11], [1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
+  call VerifyBoth(buf, 'Test_diff_04', '')
+
+  " Test 5: Add a line in the middle of file 2, remove on at the end of file 1
+  call WriteDiffFiles([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11], [1, 2, 3, 4, 4, 5, 6, 7, 8, 9, 10])
+  call VerifyBoth(buf, 'Test_diff_05', '')
+
+  " Test 6: Add a line in the middle of file 1, remove on at the end of file 2
+  call WriteDiffFiles([1, 2, 3, 4, 4, 5, 6, 7, 8, 9, 10], [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11])
+  call VerifyBoth(buf, 'Test_diff_06', '')
+
+  " Test 7 - 9: Test normal/patience/histogram diff algorithm
+  call WriteDiffFiles(['#include <stdio.h>', '', '// Frobs foo heartily', 'int frobnitz(int foo)', '{',
+      \ '    int i;', '    for(i = 0; i < 10; i++)', '    {', '        printf("Your answer is: ");',
+      \ '        printf("%d\n", foo);', '    }', '}', '', 'int fact(int n)', '{', '    if(n > 1)', '    {',
+      \ '        return fact(n-1) * n;', '    }', '    return 1;', '}', '', 'int main(int argc, char **argv)',
+      \ '{', '    frobnitz(fact(10));', '}'],
+      \ ['#include <stdio.h>', '', 'int fib(int n)', '{', '    if(n > 2)', '    {',
+      \ '        return fib(n-1) + fib(n-2);', '    }', '    return 1;', '}', '', '// Frobs foo heartily',
+      \ 'int frobnitz(int foo)', '{', '    int i;', '    for(i = 0; i < 10; i++)', '    {',
+      \ '        printf("%d\n", foo);', '    }', '}', '',
+      \ 'int main(int argc, char **argv)', '{', '    frobnitz(fib(10));', '}'])
+  call term_sendkeys(buf, ":diffupdate!\<cr>")
+  call term_sendkeys(buf, ":set diffopt+=internal\<cr>")
+  call VerifyScreenDump(buf, 'Test_diff_07', {})
+
+  call term_sendkeys(buf, ":set diffopt+=algorithm:patience\<cr>")
+  call VerifyScreenDump(buf, 'Test_diff_08', {})
+
+  call term_sendkeys(buf, ":set diffopt+=algorithm:histogram\<cr>")
+  call VerifyScreenDump(buf, 'Test_diff_09', {})
+
+  " Test 10-11: normal/indent-heuristic
+  call term_sendkeys(buf, ":set diffopt&vim\<cr>")
+  call WriteDiffFiles(['', '  def finalize(values)', '', '    values.each do |v|', '      v.finalize', '    end'],
+      \ ['', '  def finalize(values)', '', '    values.each do |v|', '      v.prepare', '    end', '',
+      \ '    values.each do |v|', '      v.finalize', '    end'])
+  call term_sendkeys(buf, ":diffupdate!\<cr>")
+  call term_sendkeys(buf, ":set diffopt+=internal\<cr>")
+  call VerifyScreenDump(buf, 'Test_diff_10', {})
+
+  call term_sendkeys(buf, ":set diffopt+=indent-heuristic\<cr>")
+  call VerifyScreenDump(buf, 'Test_diff_11', {})
+
+  " Test 12: diff the same file
+  call WriteDiffFiles([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], [1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
+  call VerifyBoth(buf, 'Test_diff_12', '')
+
+  " Test 13: diff an empty file
+  call WriteDiffFiles([], [])
+  call VerifyBoth(buf, 'Test_diff_13', '')
+
+  " Test 14: test diffopt+=icase
+  call WriteDiffFiles(['a', 'b', 'cd'], ['A', 'b', 'cDe'])
+  call VerifyBoth(buf, 'Test_diff_14', " diffopt+=filler diffopt+=icase")
+
+  " Test 15-16: test diffopt+=iwhite
+  call WriteDiffFiles(['int main()', '{', '   printf("Hello, World!");', '   return 0;', '}'],
+      \ ['int main()', '{', '   if (0)', '   {', '      printf("Hello, World!");', '      return 0;', '   }', '}'])
+  call term_sendkeys(buf, ":diffupdate!\<cr>")
+  call term_sendkeys(buf, ":set diffopt&vim diffopt+=filler diffopt+=iwhite\<cr>")
+  call VerifyScreenDump(buf, 'Test_diff_15', {})
+  call term_sendkeys(buf, ":set diffopt+=internal\<cr>")
+  call VerifyScreenDump(buf, 'Test_diff_16', {})
+
+  " clean up
+  call StopVimInTerminal(buf)
+  call delete('Xfile1')
+  call delete('Xfile2')
+endfunc
+
diff --git a/src/version.c b/src/version.c
index 73bcab1..9ba63af 100644
--- a/src/version.c
+++ b/src/version.c
@@ -795,6 +795,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    360,
+/**/
     359,
 /**/
     358,
diff --git a/src/xdiff/COPYING b/src/xdiff/COPYING
new file mode 100644
index 0000000..f3f1b3b
--- /dev/null
+++ b/src/xdiff/COPYING
@@ -0,0 +1,504 @@
+		  GNU LESSER GENERAL PUBLIC LICENSE
+		       Version 2.1, February 1999
+
+ Copyright (C) 1991, 1999 Free Software Foundation, Inc.
+     59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
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diff --git a/src/xdiff/README.txt b/src/xdiff/README.txt
new file mode 100644
index 0000000..f77893d
--- /dev/null
+++ b/src/xdiff/README.txt
@@ -0,0 +1,14 @@
+The files in this directory come from the xdiff implementation in git.
+You can find it here: https://github.com/git/git/tree/master/xdiff
+The files were last updated 2018 September 10.
+
+This is originally based on libxdiff, which can be found here:
+http://www.xmailserver.org/xdiff-lib.html
+
+The git version was used because it has been maintained and improved.
+And since it's part of git it is expected to be reliable.
+
+The code is distributed under the GNU LGPL license.  It is included in the
+COPYING file.
+
+The first work for including xdiff in Vim was done by Christian Brabandt.
diff --git a/src/xdiff/xdiff.h b/src/xdiff/xdiff.h
new file mode 100644
index 0000000..2356da5
--- /dev/null
+++ b/src/xdiff/xdiff.h
@@ -0,0 +1,142 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003  Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#if !defined(XDIFF_H)
+#define XDIFF_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* #ifdef __cplusplus */
+
+/* xpparm_t.flags */
+#define XDF_NEED_MINIMAL (1 << 0)
+
+#define XDF_IGNORE_WHITESPACE (1 << 1)
+#define XDF_IGNORE_WHITESPACE_CHANGE (1 << 2)
+#define XDF_IGNORE_WHITESPACE_AT_EOL (1 << 3)
+#define XDF_IGNORE_CR_AT_EOL (1 << 4)
+#define XDF_WHITESPACE_FLAGS (XDF_IGNORE_WHITESPACE | \
+			      XDF_IGNORE_WHITESPACE_CHANGE | \
+			      XDF_IGNORE_WHITESPACE_AT_EOL | \
+			      XDF_IGNORE_CR_AT_EOL)
+
+#define XDF_IGNORE_BLANK_LINES (1 << 7)
+
+#define XDF_PATIENCE_DIFF (1 << 14)
+#define XDF_HISTOGRAM_DIFF (1 << 15)
+#define XDF_DIFF_ALGORITHM_MASK (XDF_PATIENCE_DIFF | XDF_HISTOGRAM_DIFF)
+#define XDF_DIFF_ALG(x) ((x) & XDF_DIFF_ALGORITHM_MASK)
+
+#define XDF_INDENT_HEURISTIC (1 << 23)
+
+/* xdemitconf_t.flags */
+#define XDL_EMIT_FUNCNAMES (1 << 0)
+#define XDL_EMIT_FUNCCONTEXT (1 << 2)
+
+/* merge simplification levels */
+#define XDL_MERGE_MINIMAL 0
+#define XDL_MERGE_EAGER 1
+#define XDL_MERGE_ZEALOUS 2
+#define XDL_MERGE_ZEALOUS_ALNUM 3
+
+/* merge favor modes */
+#define XDL_MERGE_FAVOR_OURS 1
+#define XDL_MERGE_FAVOR_THEIRS 2
+#define XDL_MERGE_FAVOR_UNION 3
+
+/* merge output styles */
+#define XDL_MERGE_DIFF3 1
+
+typedef struct s_mmfile {
+	char *ptr;
+	long size;
+} mmfile_t;
+
+typedef struct s_mmbuffer {
+	char *ptr;
+	long size;
+} mmbuffer_t;
+
+typedef struct s_xpparam {
+	unsigned long flags;
+
+	/* See Documentation/diff-options.txt. */
+	char **anchors;
+	size_t anchors_nr;
+} xpparam_t;
+
+typedef struct s_xdemitcb {
+	void *priv;
+	int (*outf)(void *, mmbuffer_t *, int);
+} xdemitcb_t;
+
+typedef long (*find_func_t)(const char *line, long line_len, char *buffer, long buffer_size, void *priv);
+
+typedef int (*xdl_emit_hunk_consume_func_t)(long start_a, long count_a,
+					    long start_b, long count_b,
+					    void *cb_data);
+
+typedef struct s_xdemitconf {
+	long ctxlen;
+	long interhunkctxlen;
+	unsigned long flags;
+	find_func_t find_func;
+	void *find_func_priv;
+	xdl_emit_hunk_consume_func_t hunk_func;
+} xdemitconf_t;
+
+typedef struct s_bdiffparam {
+	long bsize;
+} bdiffparam_t;
+
+
+#define xdl_malloc(x) malloc(x)
+#define xdl_free(ptr) free(ptr)
+#define xdl_realloc(ptr,x) realloc(ptr,x)
+
+void *xdl_mmfile_first(mmfile_t *mmf, long *size);
+long xdl_mmfile_size(mmfile_t *mmf);
+
+int xdl_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
+	     xdemitconf_t const *xecfg, xdemitcb_t *ecb);
+
+typedef struct s_xmparam {
+	xpparam_t xpp;
+	int marker_size;
+	int level;
+	int favor;
+	int style;
+	const char *ancestor;	/* label for orig */
+	const char *file1;	/* label for mf1 */
+	const char *file2;	/* label for mf2 */
+} xmparam_t;
+
+#define DEFAULT_CONFLICT_MARKER_SIZE 7
+
+int xdl_merge(mmfile_t *orig, mmfile_t *mf1, mmfile_t *mf2,
+		xmparam_t const *xmp, mmbuffer_t *result);
+
+#ifdef __cplusplus
+}
+#endif /* #ifdef __cplusplus */
+
+#endif /* #if !defined(XDIFF_H) */
diff --git a/src/xdiff/xdiffi.c b/src/xdiff/xdiffi.c
new file mode 100644
index 0000000..3dc90ae
--- /dev/null
+++ b/src/xdiff/xdiffi.c
@@ -0,0 +1,1043 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003	Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#include "xinclude.h"
+
+#define XDL_MAX_COST_MIN 256
+#define XDL_HEUR_MIN_COST 256
+#define XDL_LINE_MAX (long)((1UL << (CHAR_BIT * sizeof(long) - 1)) - 1)
+#define XDL_SNAKE_CNT 20
+#define XDL_K_HEUR 4
+
+typedef struct s_xdpsplit {
+	long i1, i2;
+	int min_lo, min_hi;
+} xdpsplit_t;
+
+/*
+ * See "An O(ND) Difference Algorithm and its Variations", by Eugene Myers.
+ * Basically considers a "box" (off1, off2, lim1, lim2) and scan from both
+ * the forward diagonal starting from (off1, off2) and the backward diagonal
+ * starting from (lim1, lim2). If the K values on the same diagonal crosses
+ * returns the furthest point of reach. We might end up having to expensive
+ * cases using this algorithm is full, so a little bit of heuristic is needed
+ * to cut the search and to return a suboptimal point.
+ */
+static long xdl_split(unsigned long const *ha1, long off1, long lim1,
+		      unsigned long const *ha2, long off2, long lim2,
+		      long *kvdf, long *kvdb, int need_min, xdpsplit_t *spl,
+		      xdalgoenv_t *xenv) {
+	long dmin = off1 - lim2, dmax = lim1 - off2;
+	long fmid = off1 - off2, bmid = lim1 - lim2;
+	long odd = (fmid - bmid) & 1;
+	long fmin = fmid, fmax = fmid;
+	long bmin = bmid, bmax = bmid;
+	long ec, d, i1, i2, prev1, best, dd, v, k;
+
+	/*
+	 * Set initial diagonal values for both forward and backward path.
+	 */
+	kvdf[fmid] = off1;
+	kvdb[bmid] = lim1;
+
+	for (ec = 1;; ec++) {
+		int got_snake = 0;
+
+		/*
+		 * We need to extent the diagonal "domain" by one. If the next
+		 * values exits the box boundaries we need to change it in the
+		 * opposite direction because (max - min) must be a power of two.
+		 * Also we initialize the external K value to -1 so that we can
+		 * avoid extra conditions check inside the core loop.
+		 */
+		if (fmin > dmin)
+			kvdf[--fmin - 1] = -1;
+		else
+			++fmin;
+		if (fmax < dmax)
+			kvdf[++fmax + 1] = -1;
+		else
+			--fmax;
+
+		for (d = fmax; d >= fmin; d -= 2) {
+			if (kvdf[d - 1] >= kvdf[d + 1])
+				i1 = kvdf[d - 1] + 1;
+			else
+				i1 = kvdf[d + 1];
+			prev1 = i1;
+			i2 = i1 - d;
+			for (; i1 < lim1 && i2 < lim2 && ha1[i1] == ha2[i2]; i1++, i2++);
+			if (i1 - prev1 > xenv->snake_cnt)
+				got_snake = 1;
+			kvdf[d] = i1;
+			if (odd && bmin <= d && d <= bmax && kvdb[d] <= i1) {
+				spl->i1 = i1;
+				spl->i2 = i2;
+				spl->min_lo = spl->min_hi = 1;
+				return ec;
+			}
+		}
+
+		/*
+		 * We need to extent the diagonal "domain" by one. If the next
+		 * values exits the box boundaries we need to change it in the
+		 * opposite direction because (max - min) must be a power of two.
+		 * Also we initialize the external K value to -1 so that we can
+		 * avoid extra conditions check inside the core loop.
+		 */
+		if (bmin > dmin)
+			kvdb[--bmin - 1] = XDL_LINE_MAX;
+		else
+			++bmin;
+		if (bmax < dmax)
+			kvdb[++bmax + 1] = XDL_LINE_MAX;
+		else
+			--bmax;
+
+		for (d = bmax; d >= bmin; d -= 2) {
+			if (kvdb[d - 1] < kvdb[d + 1])
+				i1 = kvdb[d - 1];
+			else
+				i1 = kvdb[d + 1] - 1;
+			prev1 = i1;
+			i2 = i1 - d;
+			for (; i1 > off1 && i2 > off2 && ha1[i1 - 1] == ha2[i2 - 1]; i1--, i2--);
+			if (prev1 - i1 > xenv->snake_cnt)
+				got_snake = 1;
+			kvdb[d] = i1;
+			if (!odd && fmin <= d && d <= fmax && i1 <= kvdf[d]) {
+				spl->i1 = i1;
+				spl->i2 = i2;
+				spl->min_lo = spl->min_hi = 1;
+				return ec;
+			}
+		}
+
+		if (need_min)
+			continue;
+
+		/*
+		 * If the edit cost is above the heuristic trigger and if
+		 * we got a good snake, we sample current diagonals to see
+		 * if some of the, have reached an "interesting" path. Our
+		 * measure is a function of the distance from the diagonal
+		 * corner (i1 + i2) penalized with the distance from the
+		 * mid diagonal itself. If this value is above the current
+		 * edit cost times a magic factor (XDL_K_HEUR) we consider
+		 * it interesting.
+		 */
+		if (got_snake && ec > xenv->heur_min) {
+			for (best = 0, d = fmax; d >= fmin; d -= 2) {
+				dd = d > fmid ? d - fmid: fmid - d;
+				i1 = kvdf[d];
+				i2 = i1 - d;
+				v = (i1 - off1) + (i2 - off2) - dd;
+
+				if (v > XDL_K_HEUR * ec && v > best &&
+				    off1 + xenv->snake_cnt <= i1 && i1 < lim1 &&
+				    off2 + xenv->snake_cnt <= i2 && i2 < lim2) {
+					for (k = 1; ha1[i1 - k] == ha2[i2 - k]; k++)
+						if (k == xenv->snake_cnt) {
+							best = v;
+							spl->i1 = i1;
+							spl->i2 = i2;
+							break;
+						}
+				}
+			}
+			if (best > 0) {
+				spl->min_lo = 1;
+				spl->min_hi = 0;
+				return ec;
+			}
+
+			for (best = 0, d = bmax; d >= bmin; d -= 2) {
+				dd = d > bmid ? d - bmid: bmid - d;
+				i1 = kvdb[d];
+				i2 = i1 - d;
+				v = (lim1 - i1) + (lim2 - i2) - dd;
+
+				if (v > XDL_K_HEUR * ec && v > best &&
+				    off1 < i1 && i1 <= lim1 - xenv->snake_cnt &&
+				    off2 < i2 && i2 <= lim2 - xenv->snake_cnt) {
+					for (k = 0; ha1[i1 + k] == ha2[i2 + k]; k++)
+						if (k == xenv->snake_cnt - 1) {
+							best = v;
+							spl->i1 = i1;
+							spl->i2 = i2;
+							break;
+						}
+				}
+			}
+			if (best > 0) {
+				spl->min_lo = 0;
+				spl->min_hi = 1;
+				return ec;
+			}
+		}
+
+		/*
+		 * Enough is enough. We spent too much time here and now we collect
+		 * the furthest reaching path using the (i1 + i2) measure.
+		 */
+		if (ec >= xenv->mxcost) {
+			long fbest, fbest1, bbest, bbest1;
+
+			fbest = fbest1 = -1;
+			for (d = fmax; d >= fmin; d -= 2) {
+				i1 = XDL_MIN(kvdf[d], lim1);
+				i2 = i1 - d;
+				if (lim2 < i2)
+					i1 = lim2 + d, i2 = lim2;
+				if (fbest < i1 + i2) {
+					fbest = i1 + i2;
+					fbest1 = i1;
+				}
+			}
+
+			bbest = bbest1 = XDL_LINE_MAX;
+			for (d = bmax; d >= bmin; d -= 2) {
+				i1 = XDL_MAX(off1, kvdb[d]);
+				i2 = i1 - d;
+				if (i2 < off2)
+					i1 = off2 + d, i2 = off2;
+				if (i1 + i2 < bbest) {
+					bbest = i1 + i2;
+					bbest1 = i1;
+				}
+			}
+
+			if ((lim1 + lim2) - bbest < fbest - (off1 + off2)) {
+				spl->i1 = fbest1;
+				spl->i2 = fbest - fbest1;
+				spl->min_lo = 1;
+				spl->min_hi = 0;
+			} else {
+				spl->i1 = bbest1;
+				spl->i2 = bbest - bbest1;
+				spl->min_lo = 0;
+				spl->min_hi = 1;
+			}
+			return ec;
+		}
+	}
+}
+
+
+/*
+ * Rule: "Divide et Impera". Recursively split the box in sub-boxes by calling
+ * the box splitting function. Note that the real job (marking changed lines)
+ * is done in the two boundary reaching checks.
+ */
+int xdl_recs_cmp(diffdata_t *dd1, long off1, long lim1,
+		 diffdata_t *dd2, long off2, long lim2,
+		 long *kvdf, long *kvdb, int need_min, xdalgoenv_t *xenv) {
+	unsigned long const *ha1 = dd1->ha, *ha2 = dd2->ha;
+
+	/*
+	 * Shrink the box by walking through each diagonal snake (SW and NE).
+	 */
+	for (; off1 < lim1 && off2 < lim2 && ha1[off1] == ha2[off2]; off1++, off2++);
+	for (; off1 < lim1 && off2 < lim2 && ha1[lim1 - 1] == ha2[lim2 - 1]; lim1--, lim2--);
+
+	/*
+	 * If one dimension is empty, then all records on the other one must
+	 * be obviously changed.
+	 */
+	if (off1 == lim1) {
+		char *rchg2 = dd2->rchg;
+		long *rindex2 = dd2->rindex;
+
+		for (; off2 < lim2; off2++)
+			rchg2[rindex2[off2]] = 1;
+	} else if (off2 == lim2) {
+		char *rchg1 = dd1->rchg;
+		long *rindex1 = dd1->rindex;
+
+		for (; off1 < lim1; off1++)
+			rchg1[rindex1[off1]] = 1;
+	} else {
+		xdpsplit_t spl;
+		spl.i1 = spl.i2 = 0;
+
+		/*
+		 * Divide ...
+		 */
+		if (xdl_split(ha1, off1, lim1, ha2, off2, lim2, kvdf, kvdb,
+			      need_min, &spl, xenv) < 0) {
+
+			return -1;
+		}
+
+		/*
+		 * ... et Impera.
+		 */
+		if (xdl_recs_cmp(dd1, off1, spl.i1, dd2, off2, spl.i2,
+				 kvdf, kvdb, spl.min_lo, xenv) < 0 ||
+		    xdl_recs_cmp(dd1, spl.i1, lim1, dd2, spl.i2, lim2,
+				 kvdf, kvdb, spl.min_hi, xenv) < 0) {
+
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
+
+int xdl_do_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
+		xdfenv_t *xe) {
+	long ndiags;
+	long *kvd, *kvdf, *kvdb;
+	xdalgoenv_t xenv;
+	diffdata_t dd1, dd2;
+
+	if (XDF_DIFF_ALG(xpp->flags) == XDF_PATIENCE_DIFF)
+		return xdl_do_patience_diff(mf1, mf2, xpp, xe);
+
+	if (XDF_DIFF_ALG(xpp->flags) == XDF_HISTOGRAM_DIFF)
+		return xdl_do_histogram_diff(mf1, mf2, xpp, xe);
+
+	if (xdl_prepare_env(mf1, mf2, xpp, xe) < 0) {
+
+		return -1;
+	}
+
+	/*
+	 * Allocate and setup K vectors to be used by the differential algorithm.
+	 * One is to store the forward path and one to store the backward path.
+	 */
+	ndiags = xe->xdf1.nreff + xe->xdf2.nreff + 3;
+	if (!(kvd = (long *) xdl_malloc((2 * ndiags + 2) * sizeof(long)))) {
+
+		xdl_free_env(xe);
+		return -1;
+	}
+	kvdf = kvd;
+	kvdb = kvdf + ndiags;
+	kvdf += xe->xdf2.nreff + 1;
+	kvdb += xe->xdf2.nreff + 1;
+
+	xenv.mxcost = xdl_bogosqrt(ndiags);
+	if (xenv.mxcost < XDL_MAX_COST_MIN)
+		xenv.mxcost = XDL_MAX_COST_MIN;
+	xenv.snake_cnt = XDL_SNAKE_CNT;
+	xenv.heur_min = XDL_HEUR_MIN_COST;
+
+	dd1.nrec = xe->xdf1.nreff;
+	dd1.ha = xe->xdf1.ha;
+	dd1.rchg = xe->xdf1.rchg;
+	dd1.rindex = xe->xdf1.rindex;
+	dd2.nrec = xe->xdf2.nreff;
+	dd2.ha = xe->xdf2.ha;
+	dd2.rchg = xe->xdf2.rchg;
+	dd2.rindex = xe->xdf2.rindex;
+
+	if (xdl_recs_cmp(&dd1, 0, dd1.nrec, &dd2, 0, dd2.nrec,
+			 kvdf, kvdb, (xpp->flags & XDF_NEED_MINIMAL) != 0, &xenv) < 0) {
+
+		xdl_free(kvd);
+		xdl_free_env(xe);
+		return -1;
+	}
+
+	xdl_free(kvd);
+
+	return 0;
+}
+
+
+static xdchange_t *xdl_add_change(xdchange_t *xscr, long i1, long i2, long chg1, long chg2) {
+	xdchange_t *xch;
+
+	if (!(xch = (xdchange_t *) xdl_malloc(sizeof(xdchange_t))))
+		return NULL;
+
+	xch->next = xscr;
+	xch->i1 = i1;
+	xch->i2 = i2;
+	xch->chg1 = chg1;
+	xch->chg2 = chg2;
+	xch->ignore = 0;
+
+	return xch;
+}
+
+
+static int recs_match(xrecord_t *rec1, xrecord_t *rec2, long flags)
+{
+	return (rec1->ha == rec2->ha &&
+		xdl_recmatch(rec1->ptr, rec1->size,
+			     rec2->ptr, rec2->size,
+			     flags));
+}
+
+/*
+ * If a line is indented more than this, get_indent() just returns this value.
+ * This avoids having to do absurd amounts of work for data that are not
+ * human-readable text, and also ensures that the output of get_indent fits within
+ * an int.
+ */
+#define MAX_INDENT 200
+
+/*
+ * Return the amount of indentation of the specified line, treating TAB as 8
+ * columns. Return -1 if line is empty or contains only whitespace. Clamp the
+ * output value at MAX_INDENT.
+ */
+static int get_indent(xrecord_t *rec)
+{
+	long i;
+	int ret = 0;
+
+	for (i = 0; i < rec->size; i++) {
+		char c = rec->ptr[i];
+
+		if (!XDL_ISSPACE(c))
+			return ret;
+		else if (c == ' ')
+			ret += 1;
+		else if (c == '\t')
+			ret += 8 - ret % 8;
+		/* ignore other whitespace characters */
+
+		if (ret >= MAX_INDENT)
+			return MAX_INDENT;
+	}
+
+	/* The line contains only whitespace. */
+	return -1;
+}
+
+/*
+ * If more than this number of consecutive blank rows are found, just return this
+ * value. This avoids requiring O(N^2) work for pathological cases, and also
+ * ensures that the output of score_split fits in an int.
+ */
+#define MAX_BLANKS 20
+
+/* Characteristics measured about a hypothetical split position. */
+struct split_measurement {
+	/*
+	 * Is the split at the end of the file (aside from any blank lines)?
+	 */
+	int end_of_file;
+
+	/*
+	 * How much is the line immediately following the split indented (or -1 if
+	 * the line is blank):
+	 */
+	int indent;
+
+	/*
+	 * How many consecutive lines above the split are blank?
+	 */
+	int pre_blank;
+
+	/*
+	 * How much is the nearest non-blank line above the split indented (or -1
+	 * if there is no such line)?
+	 */
+	int pre_indent;
+
+	/*
+	 * How many lines after the line following the split are blank?
+	 */
+	int post_blank;
+
+	/*
+	 * How much is the nearest non-blank line after the line following the
+	 * split indented (or -1 if there is no such line)?
+	 */
+	int post_indent;
+};
+
+struct split_score {
+	/* The effective indent of this split (smaller is preferred). */
+	int effective_indent;
+
+	/* Penalty for this split (smaller is preferred). */
+	int penalty;
+};
+
+/*
+ * Fill m with information about a hypothetical split of xdf above line split.
+ */
+static void measure_split(const xdfile_t *xdf, long split,
+			  struct split_measurement *m)
+{
+	long i;
+
+	if (split >= xdf->nrec) {
+		m->end_of_file = 1;
+		m->indent = -1;
+	} else {
+		m->end_of_file = 0;
+		m->indent = get_indent(xdf->recs[split]);
+	}
+
+	m->pre_blank = 0;
+	m->pre_indent = -1;
+	for (i = split - 1; i >= 0; i--) {
+		m->pre_indent = get_indent(xdf->recs[i]);
+		if (m->pre_indent != -1)
+			break;
+		m->pre_blank += 1;
+		if (m->pre_blank == MAX_BLANKS) {
+			m->pre_indent = 0;
+			break;
+		}
+	}
+
+	m->post_blank = 0;
+	m->post_indent = -1;
+	for (i = split + 1; i < xdf->nrec; i++) {
+		m->post_indent = get_indent(xdf->recs[i]);
+		if (m->post_indent != -1)
+			break;
+		m->post_blank += 1;
+		if (m->post_blank == MAX_BLANKS) {
+			m->post_indent = 0;
+			break;
+		}
+	}
+}
+
+/*
+ * The empirically-determined weight factors used by score_split() below.
+ * Larger values means that the position is a less favorable place to split.
+ *
+ * Note that scores are only ever compared against each other, so multiplying
+ * all of these weight/penalty values by the same factor wouldn't change the
+ * heuristic's behavior. Still, we need to set that arbitrary scale *somehow*.
+ * In practice, these numbers are chosen to be large enough that they can be
+ * adjusted relative to each other with sufficient precision despite using
+ * integer math.
+ */
+
+/* Penalty if there are no non-blank lines before the split */
+#define START_OF_FILE_PENALTY 1
+
+/* Penalty if there are no non-blank lines after the split */
+#define END_OF_FILE_PENALTY 21
+
+/* Multiplier for the number of blank lines around the split */
+#define TOTAL_BLANK_WEIGHT (-30)
+
+/* Multiplier for the number of blank lines after the split */
+#define POST_BLANK_WEIGHT 6
+
+/*
+ * Penalties applied if the line is indented more than its predecessor
+ */
+#define RELATIVE_INDENT_PENALTY (-4)
+#define RELATIVE_INDENT_WITH_BLANK_PENALTY 10
+
+/*
+ * Penalties applied if the line is indented less than both its predecessor and
+ * its successor
+ */
+#define RELATIVE_OUTDENT_PENALTY 24
+#define RELATIVE_OUTDENT_WITH_BLANK_PENALTY 17
+
+/*
+ * Penalties applied if the line is indented less than its predecessor but not
+ * less than its successor
+ */
+#define RELATIVE_DEDENT_PENALTY 23
+#define RELATIVE_DEDENT_WITH_BLANK_PENALTY 17
+
+/*
+ * We only consider whether the sum of the effective indents for splits are
+ * less than (-1), equal to (0), or greater than (+1) each other. The resulting
+ * value is multiplied by the following weight and combined with the penalty to
+ * determine the better of two scores.
+ */
+#define INDENT_WEIGHT 60
+
+/*
+ * How far do we slide a hunk at most?
+ */
+#define INDENT_HEURISTIC_MAX_SLIDING 100
+
+/*
+ * Compute a badness score for the hypothetical split whose measurements are
+ * stored in m. The weight factors were determined empirically using the tools and
+ * corpus described in
+ *
+ *     https://github.com/mhagger/diff-slider-tools
+ *
+ * Also see that project if you want to improve the weights based on, for example,
+ * a larger or more diverse corpus.
+ */
+static void score_add_split(const struct split_measurement *m, struct split_score *s)
+{
+	/*
+	 * A place to accumulate penalty factors (positive makes this index more
+	 * favored):
+	 */
+	int post_blank, total_blank, indent, any_blanks;
+
+	if (m->pre_indent == -1 && m->pre_blank == 0)
+		s->penalty += START_OF_FILE_PENALTY;
+
+	if (m->end_of_file)
+		s->penalty += END_OF_FILE_PENALTY;
+
+	/*
+	 * Set post_blank to the number of blank lines following the split,
+	 * including the line immediately after the split:
+	 */
+	post_blank = (m->indent == -1) ? 1 + m->post_blank : 0;
+	total_blank = m->pre_blank + post_blank;
+
+	/* Penalties based on nearby blank lines: */
+	s->penalty += TOTAL_BLANK_WEIGHT * total_blank;
+	s->penalty += POST_BLANK_WEIGHT * post_blank;
+
+	if (m->indent != -1)
+		indent = m->indent;
+	else
+		indent = m->post_indent;
+
+	any_blanks = (total_blank != 0);
+
+	/* Note that the effective indent is -1 at the end of the file: */
+	s->effective_indent += indent;
+
+	if (indent == -1) {
+		/* No additional adjustments needed. */
+	} else if (m->pre_indent == -1) {
+		/* No additional adjustments needed. */
+	} else if (indent > m->pre_indent) {
+		/*
+		 * The line is indented more than its predecessor.
+		 */
+		s->penalty += any_blanks ?
+			RELATIVE_INDENT_WITH_BLANK_PENALTY :
+			RELATIVE_INDENT_PENALTY;
+	} else if (indent == m->pre_indent) {
+		/*
+		 * The line has the same indentation level as its predecessor.
+		 * No additional adjustments needed.
+		 */
+	} else {
+		/*
+		 * The line is indented less than its predecessor. It could be
+		 * the block terminator of the previous block, but it could
+		 * also be the start of a new block (e.g., an "else" block, or
+		 * maybe the previous block didn't have a block terminator).
+		 * Try to distinguish those cases based on what comes next:
+		 */
+		if (m->post_indent != -1 && m->post_indent > indent) {
+			/*
+			 * The following line is indented more. So it is likely
+			 * that this line is the start of a block.
+			 */
+			s->penalty += any_blanks ?
+				RELATIVE_OUTDENT_WITH_BLANK_PENALTY :
+				RELATIVE_OUTDENT_PENALTY;
+		} else {
+			/*
+			 * That was probably the end of a block.
+			 */
+			s->penalty += any_blanks ?
+				RELATIVE_DEDENT_WITH_BLANK_PENALTY :
+				RELATIVE_DEDENT_PENALTY;
+		}
+	}
+}
+
+static int score_cmp(struct split_score *s1, struct split_score *s2)
+{
+	/* -1 if s1.effective_indent < s2->effective_indent, etc. */
+	int cmp_indents = ((s1->effective_indent > s2->effective_indent) -
+			   (s1->effective_indent < s2->effective_indent));
+
+	return INDENT_WEIGHT * cmp_indents + (s1->penalty - s2->penalty);
+}
+
+/*
+ * Represent a group of changed lines in an xdfile_t (i.e., a contiguous group
+ * of lines that was inserted or deleted from the corresponding version of the
+ * file). We consider there to be such a group at the beginning of the file, at
+ * the end of the file, and between any two unchanged lines, though most such
+ * groups will usually be empty.
+ *
+ * If the first line in a group is equal to the line following the group, then
+ * the group can be slid down. Similarly, if the last line in a group is equal
+ * to the line preceding the group, then the group can be slid up. See
+ * group_slide_down() and group_slide_up().
+ *
+ * Note that loops that are testing for changed lines in xdf->rchg do not need
+ * index bounding since the array is prepared with a zero at position -1 and N.
+ */
+struct xdlgroup {
+	/*
+	 * The index of the first changed line in the group, or the index of
+	 * the unchanged line above which the (empty) group is located.
+	 */
+	long start;
+
+	/*
+	 * The index of the first unchanged line after the group. For an empty
+	 * group, end is equal to start.
+	 */
+	long end;
+};
+
+/*
+ * Initialize g to point at the first group in xdf.
+ */
+static void group_init(xdfile_t *xdf, struct xdlgroup *g)
+{
+	g->start = g->end = 0;
+	while (xdf->rchg[g->end])
+		g->end++;
+}
+
+/*
+ * Move g to describe the next (possibly empty) group in xdf and return 0. If g
+ * is already at the end of the file, do nothing and return -1.
+ */
+static inline int group_next(xdfile_t *xdf, struct xdlgroup *g)
+{
+	if (g->end == xdf->nrec)
+		return -1;
+
+	g->start = g->end + 1;
+	for (g->end = g->start; xdf->rchg[g->end]; g->end++)
+		;
+
+	return 0;
+}
+
+/*
+ * Move g to describe the previous (possibly empty) group in xdf and return 0.
+ * If g is already at the beginning of the file, do nothing and return -1.
+ */
+static inline int group_previous(xdfile_t *xdf, struct xdlgroup *g)
+{
+	if (g->start == 0)
+		return -1;
+
+	g->end = g->start - 1;
+	for (g->start = g->end; xdf->rchg[g->start - 1]; g->start--)
+		;
+
+	return 0;
+}
+
+/*
+ * If g can be slid toward the end of the file, do so, and if it bumps into a
+ * following group, expand this group to include it. Return 0 on success or -1
+ * if g cannot be slid down.
+ */
+static int group_slide_down(xdfile_t *xdf, struct xdlgroup *g, long flags)
+{
+	if (g->end < xdf->nrec &&
+	    recs_match(xdf->recs[g->start], xdf->recs[g->end], flags)) {
+		xdf->rchg[g->start++] = 0;
+		xdf->rchg[g->end++] = 1;
+
+		while (xdf->rchg[g->end])
+			g->end++;
+
+		return 0;
+	} else {
+		return -1;
+	}
+}
+
+/*
+ * If g can be slid toward the beginning of the file, do so, and if it bumps
+ * into a previous group, expand this group to include it. Return 0 on success
+ * or -1 if g cannot be slid up.
+ */
+static int group_slide_up(xdfile_t *xdf, struct xdlgroup *g, long flags)
+{
+	if (g->start > 0 &&
+	    recs_match(xdf->recs[g->start - 1], xdf->recs[g->end - 1], flags)) {
+		xdf->rchg[--g->start] = 1;
+		xdf->rchg[--g->end] = 0;
+
+		while (xdf->rchg[g->start - 1])
+			g->start--;
+
+		return 0;
+	} else {
+		return -1;
+	}
+}
+
+static void xdl_bug(const char *msg)
+{
+	fprintf(stderr, "BUG: %s\n", msg);
+	exit(1);
+}
+
+/*
+ * Move back and forward change groups for a consistent and pretty diff output.
+ * This also helps in finding joinable change groups and reducing the diff
+ * size.
+ */
+int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
+	struct xdlgroup g, go;
+	long earliest_end, end_matching_other;
+	long groupsize;
+
+	group_init(xdf, &g);
+	group_init(xdfo, &go);
+
+	while (1) {
+		/* If the group is empty in the to-be-compacted file, skip it: */
+		if (g.end == g.start)
+			goto next;
+
+		/*
+		 * Now shift the change up and then down as far as possible in
+		 * each direction. If it bumps into any other changes, merge them.
+		 */
+		do {
+			groupsize = g.end - g.start;
+
+			/*
+			 * Keep track of the last "end" index that causes this
+			 * group to align with a group of changed lines in the
+			 * other file. -1 indicates that we haven't found such
+			 * a match yet:
+			 */
+			end_matching_other = -1;
+
+			/* Shift the group backward as much as possible: */
+			while (!group_slide_up(xdf, &g, flags))
+				if (group_previous(xdfo, &go))
+					xdl_bug("group sync broken sliding up");
+
+			/*
+			 * This is this highest that this group can be shifted.
+			 * Record its end index:
+			 */
+			earliest_end = g.end;
+
+			if (go.end > go.start)
+				end_matching_other = g.end;
+
+			/* Now shift the group forward as far as possible: */
+			while (1) {
+				if (group_slide_down(xdf, &g, flags))
+					break;
+				if (group_next(xdfo, &go))
+					xdl_bug("group sync broken sliding down");
+
+				if (go.end > go.start)
+					end_matching_other = g.end;
+			}
+		} while (groupsize != g.end - g.start);
+
+		/*
+		 * If the group can be shifted, then we can possibly use this
+		 * freedom to produce a more intuitive diff.
+		 *
+		 * The group is currently shifted as far down as possible, so the
+		 * heuristics below only have to handle upwards shifts.
+		 */
+
+		if (g.end == earliest_end) {
+			/* no shifting was possible */
+		} else if (end_matching_other != -1) {
+			/*
+			 * Move the possibly merged group of changes back to line
+			 * up with the last group of changes from the other file
+			 * that it can align with.
+			 */
+			while (go.end == go.start) {
+				if (group_slide_up(xdf, &g, flags))
+					xdl_bug("match disappeared");
+				if (group_previous(xdfo, &go))
+					xdl_bug("group sync broken sliding to match");
+			}
+		} else if (flags & XDF_INDENT_HEURISTIC) {
+			/*
+			 * Indent heuristic: a group of pure add/delete lines
+			 * implies two splits, one between the end of the "before"
+			 * context and the start of the group, and another between
+			 * the end of the group and the beginning of the "after"
+			 * context. Some splits are aesthetically better and some
+			 * are worse. We compute a badness "score" for each split,
+			 * and add the scores for the two splits to define a
+			 * "score" for each position that the group can be shifted
+			 * to. Then we pick the shift with the lowest score.
+			 */
+			long shift, best_shift = -1;
+			struct split_score best_score;
+
+			shift = earliest_end;
+			if (g.end - groupsize - 1 > shift)
+				shift = g.end - groupsize - 1;
+			if (g.end - INDENT_HEURISTIC_MAX_SLIDING > shift)
+				shift = g.end - INDENT_HEURISTIC_MAX_SLIDING;
+			for (; shift <= g.end; shift++) {
+				struct split_measurement m;
+				struct split_score score = {0, 0};
+
+				measure_split(xdf, shift, &m);
+				score_add_split(&m, &score);
+				measure_split(xdf, shift - groupsize, &m);
+				score_add_split(&m, &score);
+				if (best_shift == -1 ||
+				    score_cmp(&score, &best_score) <= 0) {
+					best_score.effective_indent = score.effective_indent;
+					best_score.penalty = score.penalty;
+					best_shift = shift;
+				}
+			}
+
+			while (g.end > best_shift) {
+				if (group_slide_up(xdf, &g, flags))
+					xdl_bug("best shift unreached");
+				if (group_previous(xdfo, &go))
+					xdl_bug("group sync broken sliding to blank line");
+			}
+		}
+
+	next:
+		/* Move past the just-processed group: */
+		if (group_next(xdf, &g))
+			break;
+		if (group_next(xdfo, &go))
+			xdl_bug("group sync broken moving to next group");
+	}
+
+	if (!group_next(xdfo, &go))
+		xdl_bug("group sync broken at end of file");
+
+	return 0;
+}
+
+
+int xdl_build_script(xdfenv_t *xe, xdchange_t **xscr) {
+	xdchange_t *cscr = NULL, *xch;
+	char *rchg1 = xe->xdf1.rchg, *rchg2 = xe->xdf2.rchg;
+	long i1, i2, l1, l2;
+
+	/*
+	 * Trivial. Collects "groups" of changes and creates an edit script.
+	 */
+	for (i1 = xe->xdf1.nrec, i2 = xe->xdf2.nrec; i1 >= 0 || i2 >= 0; i1--, i2--)
+		if (rchg1[i1 - 1] || rchg2[i2 - 1]) {
+			for (l1 = i1; rchg1[i1 - 1]; i1--);
+			for (l2 = i2; rchg2[i2 - 1]; i2--);
+
+			if (!(xch = xdl_add_change(cscr, i1, i2, l1 - i1, l2 - i2))) {
+				xdl_free_script(cscr);
+				return -1;
+			}
+			cscr = xch;
+		}
+
+	*xscr = cscr;
+
+	return 0;
+}
+
+
+void xdl_free_script(xdchange_t *xscr) {
+	xdchange_t *xch;
+
+	while ((xch = xscr) != NULL) {
+		xscr = xscr->next;
+		xdl_free(xch);
+	}
+}
+
+static int xdl_call_hunk_func(xdfenv_t *xe UNUSED, xdchange_t *xscr, xdemitcb_t *ecb,
+			      xdemitconf_t const *xecfg)
+{
+	xdchange_t *xch, *xche;
+
+	for (xch = xscr; xch; xch = xche->next) {
+		xche = xdl_get_hunk(&xch, xecfg);
+		if (!xch)
+			break;
+		if (xecfg->hunk_func(xch->i1, xche->i1 + xche->chg1 - xch->i1,
+				     xch->i2, xche->i2 + xche->chg2 - xch->i2,
+				     ecb->priv) < 0)
+			return -1;
+	}
+	return 0;
+}
+
+static void xdl_mark_ignorable(xdchange_t *xscr, xdfenv_t *xe, long flags)
+{
+	xdchange_t *xch;
+
+	for (xch = xscr; xch; xch = xch->next) {
+		int ignore = 1;
+		xrecord_t **rec;
+		long i;
+
+		rec = &xe->xdf1.recs[xch->i1];
+		for (i = 0; i < xch->chg1 && ignore; i++)
+			ignore = xdl_blankline(rec[i]->ptr, rec[i]->size, flags);
+
+		rec = &xe->xdf2.recs[xch->i2];
+		for (i = 0; i < xch->chg2 && ignore; i++)
+			ignore = xdl_blankline(rec[i]->ptr, rec[i]->size, flags);
+
+		xch->ignore = ignore;
+	}
+}
+
+int xdl_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
+	     xdemitconf_t const *xecfg, xdemitcb_t *ecb) {
+	xdchange_t *xscr;
+	xdfenv_t xe;
+	emit_func_t ef = xecfg->hunk_func ? xdl_call_hunk_func : xdl_emit_diff;
+
+	if (xdl_do_diff(mf1, mf2, xpp, &xe) < 0) {
+
+		return -1;
+	}
+	if (xdl_change_compact(&xe.xdf1, &xe.xdf2, xpp->flags) < 0 ||
+	    xdl_change_compact(&xe.xdf2, &xe.xdf1, xpp->flags) < 0 ||
+	    xdl_build_script(&xe, &xscr) < 0) {
+
+		xdl_free_env(&xe);
+		return -1;
+	}
+	if (xscr) {
+		if (xpp->flags & XDF_IGNORE_BLANK_LINES)
+			xdl_mark_ignorable(xscr, &xe, xpp->flags);
+
+		if (ef(&xe, xscr, ecb, xecfg) < 0) {
+
+			xdl_free_script(xscr);
+			xdl_free_env(&xe);
+			return -1;
+		}
+		xdl_free_script(xscr);
+	}
+	xdl_free_env(&xe);
+
+	return 0;
+}
diff --git a/src/xdiff/xdiffi.h b/src/xdiff/xdiffi.h
new file mode 100644
index 0000000..8f1c7c8
--- /dev/null
+++ b/src/xdiff/xdiffi.h
@@ -0,0 +1,64 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003  Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#if !defined(XDIFFI_H)
+#define XDIFFI_H
+
+
+typedef struct s_diffdata {
+	long nrec;
+	unsigned long const *ha;
+	long *rindex;
+	char *rchg;
+} diffdata_t;
+
+typedef struct s_xdalgoenv {
+	long mxcost;
+	long snake_cnt;
+	long heur_min;
+} xdalgoenv_t;
+
+typedef struct s_xdchange {
+	struct s_xdchange *next;
+	long i1, i2;
+	long chg1, chg2;
+	int ignore;
+} xdchange_t;
+
+
+
+int xdl_recs_cmp(diffdata_t *dd1, long off1, long lim1,
+		 diffdata_t *dd2, long off2, long lim2,
+		 long *kvdf, long *kvdb, int need_min, xdalgoenv_t *xenv);
+int xdl_do_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
+		xdfenv_t *xe);
+int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags);
+int xdl_build_script(xdfenv_t *xe, xdchange_t **xscr);
+void xdl_free_script(xdchange_t *xscr);
+int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
+		  xdemitconf_t const *xecfg);
+int xdl_do_patience_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
+		xdfenv_t *env);
+int xdl_do_histogram_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
+		xdfenv_t *env);
+
+#endif /* #if !defined(XDIFFI_H) */
diff --git a/src/xdiff/xemit.c b/src/xdiff/xemit.c
new file mode 100644
index 0000000..718b3ae
--- /dev/null
+++ b/src/xdiff/xemit.c
@@ -0,0 +1,312 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003	Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#include "xinclude.h"
+
+static long xdl_get_rec(xdfile_t *xdf, long ri, char const **rec) {
+
+	*rec = xdf->recs[ri]->ptr;
+
+	return xdf->recs[ri]->size;
+}
+
+
+static int xdl_emit_record(xdfile_t *xdf, long ri, char const *pre, xdemitcb_t *ecb) {
+	long size, psize = strlen(pre);
+	char const *rec;
+
+	size = xdl_get_rec(xdf, ri, &rec);
+	if (xdl_emit_diffrec(rec, size, pre, psize, ecb) < 0) {
+
+		return -1;
+	}
+
+	return 0;
+}
+
+
+/*
+ * Starting at the passed change atom, find the latest change atom to be included
+ * inside the differential hunk according to the specified configuration.
+ * Also advance xscr if the first changes must be discarded.
+ */
+xdchange_t *xdl_get_hunk(xdchange_t **xscr, xdemitconf_t const *xecfg)
+{
+	xdchange_t *xch, *xchp, *lxch;
+	long max_common = 2 * xecfg->ctxlen + xecfg->interhunkctxlen;
+	long max_ignorable = xecfg->ctxlen;
+	unsigned long ignored = 0; /* number of ignored blank lines */
+
+	/* remove ignorable changes that are too far before other changes */
+	for (xchp = *xscr; xchp && xchp->ignore; xchp = xchp->next) {
+		xch = xchp->next;
+
+		if (xch == NULL ||
+		    xch->i1 - (xchp->i1 + xchp->chg1) >= max_ignorable)
+			*xscr = xch;
+	}
+
+	if (*xscr == NULL)
+		return NULL;
+
+	lxch = *xscr;
+
+	for (xchp = *xscr, xch = xchp->next; xch; xchp = xch, xch = xch->next) {
+		long distance = xch->i1 - (xchp->i1 + xchp->chg1);
+		if (distance > max_common)
+			break;
+
+		if (distance < max_ignorable && (!xch->ignore || lxch == xchp)) {
+			lxch = xch;
+			ignored = 0;
+		} else if (distance < max_ignorable && xch->ignore) {
+			ignored += xch->chg2;
+		} else if (lxch != xchp &&
+			   xch->i1 + (long)ignored - (lxch->i1 + lxch->chg1) > max_common) {
+			break;
+		} else if (!xch->ignore) {
+			lxch = xch;
+			ignored = 0;
+		} else {
+			ignored += xch->chg2;
+		}
+	}
+
+	return lxch;
+}
+
+
+static long def_ff(const char *rec, long len, char *buf, long sz, void *priv UNUSED)
+{
+	if (len > 0 &&
+			(isalpha((unsigned char)*rec) || /* identifier? */
+			 *rec == '_' || /* also identifier? */
+			 *rec == '$')) { /* identifiers from VMS and other esoterico */
+		if (len > sz)
+			len = sz;
+		while (0 < len && isspace((unsigned char)rec[len - 1]))
+			len--;
+		memcpy(buf, rec, len);
+		return len;
+	}
+	return -1;
+}
+
+static long match_func_rec(xdfile_t *xdf, xdemitconf_t const *xecfg, long ri,
+			   char *buf, long sz)
+{
+	const char *rec;
+	long len = xdl_get_rec(xdf, ri, &rec);
+	if (!xecfg->find_func)
+		return def_ff(rec, len, buf, sz, xecfg->find_func_priv);
+	return xecfg->find_func(rec, len, buf, sz, xecfg->find_func_priv);
+}
+
+static int is_func_rec(xdfile_t *xdf, xdemitconf_t const *xecfg, long ri)
+{
+	char dummy[1];
+	return match_func_rec(xdf, xecfg, ri, dummy, sizeof(dummy)) >= 0;
+}
+
+struct func_line {
+	long len;
+	char buf[80];
+};
+
+static long get_func_line(xdfenv_t *xe, xdemitconf_t const *xecfg,
+			  struct func_line *func_line, long start, long limit)
+{
+	long l, size, step = (start > limit) ? -1 : 1;
+	char *buf, dummy[1];
+
+	buf = func_line ? func_line->buf : dummy;
+	size = func_line ? sizeof(func_line->buf) : sizeof(dummy);
+
+	for (l = start; l != limit && 0 <= l && l < xe->xdf1.nrec; l += step) {
+		long len = match_func_rec(&xe->xdf1, xecfg, l, buf, size);
+		if (len >= 0) {
+			if (func_line)
+				func_line->len = len;
+			return l;
+		}
+	}
+	return -1;
+}
+
+static int is_empty_rec(xdfile_t *xdf, long ri)
+{
+	const char *rec;
+	long len = xdl_get_rec(xdf, ri, &rec);
+
+	while (len > 0 && XDL_ISSPACE(*rec)) {
+		rec++;
+		len--;
+	}
+	return !len;
+}
+
+int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
+		  xdemitconf_t const *xecfg) {
+	long s1, s2, e1, e2, lctx;
+	xdchange_t *xch, *xche;
+	long funclineprev = -1;
+	struct func_line func_line = { 0 };
+
+	for (xch = xscr; xch; xch = xche->next) {
+		xche = xdl_get_hunk(&xch, xecfg);
+		if (!xch)
+			break;
+
+		s1 = XDL_MAX(xch->i1 - xecfg->ctxlen, 0);
+		s2 = XDL_MAX(xch->i2 - xecfg->ctxlen, 0);
+
+		if (xecfg->flags & XDL_EMIT_FUNCCONTEXT) {
+			long fs1, i1 = xch->i1;
+
+			/* Appended chunk? */
+			if (i1 >= xe->xdf1.nrec) {
+				long i2 = xch->i2;
+
+				/*
+				 * We don't need additional context if
+				 * a whole function was added.
+				 */
+				while (i2 < xe->xdf2.nrec) {
+					if (is_func_rec(&xe->xdf2, xecfg, i2))
+						goto post_context_calculation;
+					i2++;
+				}
+
+				/*
+				 * Otherwise get more context from the
+				 * pre-image.
+				 */
+				i1 = xe->xdf1.nrec - 1;
+			}
+
+			fs1 = get_func_line(xe, xecfg, NULL, i1, -1);
+			while (fs1 > 0 && !is_empty_rec(&xe->xdf1, fs1 - 1) &&
+			       !is_func_rec(&xe->xdf1, xecfg, fs1 - 1))
+				fs1--;
+			if (fs1 < 0)
+				fs1 = 0;
+			if (fs1 < s1) {
+				s2 -= s1 - fs1;
+				s1 = fs1;
+			}
+		}
+
+ post_context_calculation:
+		lctx = xecfg->ctxlen;
+		lctx = XDL_MIN(lctx, xe->xdf1.nrec - (xche->i1 + xche->chg1));
+		lctx = XDL_MIN(lctx, xe->xdf2.nrec - (xche->i2 + xche->chg2));
+
+		e1 = xche->i1 + xche->chg1 + lctx;
+		e2 = xche->i2 + xche->chg2 + lctx;
+
+		if (xecfg->flags & XDL_EMIT_FUNCCONTEXT) {
+			long fe1 = get_func_line(xe, xecfg, NULL,
+						 xche->i1 + xche->chg1,
+						 xe->xdf1.nrec);
+			while (fe1 > 0 && is_empty_rec(&xe->xdf1, fe1 - 1))
+				fe1--;
+			if (fe1 < 0)
+				fe1 = xe->xdf1.nrec;
+			if (fe1 > e1) {
+				e2 += fe1 - e1;
+				e1 = fe1;
+			}
+
+			/*
+			 * Overlap with next change?  Then include it
+			 * in the current hunk and start over to find
+			 * its new end.
+			 */
+			if (xche->next) {
+				long l = XDL_MIN(xche->next->i1,
+						 xe->xdf1.nrec - 1);
+				if (l - xecfg->ctxlen <= e1 ||
+				    get_func_line(xe, xecfg, NULL, l, e1) < 0) {
+					xche = xche->next;
+					goto post_context_calculation;
+				}
+			}
+		}
+
+		/*
+		 * Emit current hunk header.
+		 */
+
+		if (xecfg->flags & XDL_EMIT_FUNCNAMES) {
+			get_func_line(xe, xecfg, &func_line,
+				      s1 - 1, funclineprev);
+			funclineprev = s1 - 1;
+		}
+		if (xdl_emit_hunk_hdr(s1 + 1, e1 - s1, s2 + 1, e2 - s2,
+				      func_line.buf, func_line.len, ecb) < 0)
+			return -1;
+
+		/*
+		 * Emit pre-context.
+		 */
+		for (; s2 < xch->i2; s2++)
+			if (xdl_emit_record(&xe->xdf2, s2, " ", ecb) < 0)
+				return -1;
+
+		for (s1 = xch->i1, s2 = xch->i2;; xch = xch->next) {
+			/*
+			 * Merge previous with current change atom.
+			 */
+			for (; s1 < xch->i1 && s2 < xch->i2; s1++, s2++)
+				if (xdl_emit_record(&xe->xdf2, s2, " ", ecb) < 0)
+					return -1;
+
+			/*
+			 * Removes lines from the first file.
+			 */
+			for (s1 = xch->i1; s1 < xch->i1 + xch->chg1; s1++)
+				if (xdl_emit_record(&xe->xdf1, s1, "-", ecb) < 0)
+					return -1;
+
+			/*
+			 * Adds lines from the second file.
+			 */
+			for (s2 = xch->i2; s2 < xch->i2 + xch->chg2; s2++)
+				if (xdl_emit_record(&xe->xdf2, s2, "+", ecb) < 0)
+					return -1;
+
+			if (xch == xche)
+				break;
+			s1 = xch->i1 + xch->chg1;
+			s2 = xch->i2 + xch->chg2;
+		}
+
+		/*
+		 * Emit post-context.
+		 */
+		for (s2 = xche->i2 + xche->chg2; s2 < e2; s2++)
+			if (xdl_emit_record(&xe->xdf2, s2, " ", ecb) < 0)
+				return -1;
+	}
+
+	return 0;
+}
diff --git a/src/xdiff/xemit.h b/src/xdiff/xemit.h
new file mode 100644
index 0000000..1b9887e
--- /dev/null
+++ b/src/xdiff/xemit.h
@@ -0,0 +1,36 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003  Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#if !defined(XEMIT_H)
+#define XEMIT_H
+
+
+typedef int (*emit_func_t)(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
+			   xdemitconf_t const *xecfg);
+
+xdchange_t *xdl_get_hunk(xdchange_t **xscr, xdemitconf_t const *xecfg);
+int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
+		  xdemitconf_t const *xecfg);
+
+
+
+#endif /* #if !defined(XEMIT_H) */
diff --git a/src/xdiff/xhistogram.c b/src/xdiff/xhistogram.c
new file mode 100644
index 0000000..3fb8974
--- /dev/null
+++ b/src/xdiff/xhistogram.c
@@ -0,0 +1,386 @@
+/*
+ * Copyright (C) 2010, Google Inc.
+ * and other copyright owners as documented in JGit's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "xinclude.h"
+#include "xtypes.h"
+#include "xdiff.h"
+
+#define MAX_PTR	INT_MAX
+#define MAX_CNT	INT_MAX
+
+#define LINE_END(n) (line##n + count##n - 1)
+#define LINE_END_PTR(n) (*line##n + *count##n - 1)
+
+struct histindex {
+	struct record {
+		unsigned int ptr, cnt;
+		struct record *next;
+	} **records, /* an occurrence */
+	  **line_map; /* map of line to record chain */
+	chastore_t rcha;
+	unsigned int *next_ptrs;
+	unsigned int table_bits,
+		     records_size,
+		     line_map_size;
+
+	unsigned int max_chain_length,
+		     key_shift,
+		     ptr_shift;
+
+	unsigned int cnt,
+		     has_common;
+
+	xdfenv_t *env;
+	xpparam_t const *xpp;
+};
+
+struct region {
+	unsigned int begin1, end1;
+	unsigned int begin2, end2;
+};
+
+#define LINE_MAP(i, a) (i->line_map[(a) - i->ptr_shift])
+
+#define NEXT_PTR(index, ptr) \
+	(index->next_ptrs[(ptr) - index->ptr_shift])
+
+#define CNT(index, ptr) \
+	((LINE_MAP(index, ptr))->cnt)
+
+#define REC(env, s, l) \
+	(env->xdf##s.recs[l - 1])
+
+static int cmp_recs(xpparam_t const *xpp,
+	xrecord_t *r1, xrecord_t *r2)
+{
+	return r1->ha == r2->ha &&
+		xdl_recmatch(r1->ptr, r1->size, r2->ptr, r2->size,
+			    xpp->flags);
+}
+
+#define CMP_ENV(xpp, env, s1, l1, s2, l2) \
+	(cmp_recs(xpp, REC(env, s1, l1), REC(env, s2, l2)))
+
+#define CMP(i, s1, l1, s2, l2) \
+	(cmp_recs(i->xpp, REC(i->env, s1, l1), REC(i->env, s2, l2)))
+
+#define TABLE_HASH(index, side, line) \
+	XDL_HASHLONG((REC(index->env, side, line))->ha, index->table_bits)
+
+static int scanA(struct histindex *index, int line1, int count1)
+{
+	int ptr, tbl_idx;
+	unsigned int chain_len;
+	struct record **rec_chain, *rec;
+
+	for (ptr = LINE_END(1); line1 <= ptr; ptr--) {
+		tbl_idx = TABLE_HASH(index, 1, ptr);
+		rec_chain = index->records + tbl_idx;
+		rec = *rec_chain;
+
+		chain_len = 0;
+		while (rec) {
+			if (CMP(index, 1, rec->ptr, 1, ptr)) {
+				/*
+				 * ptr is identical to another element. Insert
+				 * it onto the front of the existing element
+				 * chain.
+				 */
+				NEXT_PTR(index, ptr) = rec->ptr;
+				rec->ptr = ptr;
+				/* cap rec->cnt at MAX_CNT */
+				rec->cnt = XDL_MIN(MAX_CNT, rec->cnt + 1);
+				LINE_MAP(index, ptr) = rec;
+				goto continue_scan;
+			}
+
+			rec = rec->next;
+			chain_len++;
+		}
+
+		if (chain_len == index->max_chain_length)
+			return -1;
+
+		/*
+		 * This is the first time we have ever seen this particular
+		 * element in the sequence. Construct a new chain for it.
+		 */
+		if (!(rec = xdl_cha_alloc(&index->rcha)))
+			return -1;
+		rec->ptr = ptr;
+		rec->cnt = 1;
+		rec->next = *rec_chain;
+		*rec_chain = rec;
+		LINE_MAP(index, ptr) = rec;
+
+continue_scan:
+		; /* no op */
+	}
+
+	return 0;
+}
+
+static int try_lcs(struct histindex *index, struct region *lcs, int b_ptr,
+	int line1, int count1, int line2, int count2)
+{
+	unsigned int b_next = b_ptr + 1;
+	struct record *rec = index->records[TABLE_HASH(index, 2, b_ptr)];
+	unsigned int as, ae, bs, be, np, rc;
+	int should_break;
+
+	for (; rec; rec = rec->next) {
+		if (rec->cnt > index->cnt) {
+			if (!index->has_common)
+				index->has_common = CMP(index, 1, rec->ptr, 2, b_ptr);
+			continue;
+		}
+
+		as = rec->ptr;
+		if (!CMP(index, 1, as, 2, b_ptr))
+			continue;
+
+		index->has_common = 1;
+		for (;;) {
+			should_break = 0;
+			np = NEXT_PTR(index, as);
+			bs = b_ptr;
+			ae = as;
+			be = bs;
+			rc = rec->cnt;
+
+			while (line1 < (int)as && line2 < (int)bs
+				&& CMP(index, 1, as - 1, 2, bs - 1)) {
+				as--;
+				bs--;
+				if (1 < rc)
+					rc = XDL_MIN(rc, CNT(index, as));
+			}
+			while ((int)ae < LINE_END(1) && (int)be < LINE_END(2)
+				&& CMP(index, 1, ae + 1, 2, be + 1)) {
+				ae++;
+				be++;
+				if (1 < rc)
+					rc = XDL_MIN(rc, CNT(index, ae));
+			}
+
+			if (b_next <= be)
+				b_next = be + 1;
+			if (lcs->end1 - lcs->begin1 < ae - as || rc < index->cnt) {
+				lcs->begin1 = as;
+				lcs->begin2 = bs;
+				lcs->end1 = ae;
+				lcs->end2 = be;
+				index->cnt = rc;
+			}
+
+			if (np == 0)
+				break;
+
+			while (np <= ae) {
+				np = NEXT_PTR(index, np);
+				if (np == 0) {
+					should_break = 1;
+					break;
+				}
+			}
+
+			if (should_break)
+				break;
+
+			as = np;
+		}
+	}
+	return b_next;
+}
+
+static int fall_back_to_classic_diff(xpparam_t const *xpp, xdfenv_t *env,
+		int line1, int count1, int line2, int count2)
+{
+	xpparam_t xpparam;
+	xpparam.flags = xpp->flags & ~XDF_DIFF_ALGORITHM_MASK;
+
+	return xdl_fall_back_diff(env, &xpparam,
+				  line1, count1, line2, count2);
+}
+
+static inline void free_index(struct histindex *index)
+{
+	xdl_free(index->records);
+	xdl_free(index->line_map);
+	xdl_free(index->next_ptrs);
+	xdl_cha_free(&index->rcha);
+}
+
+static int find_lcs(xpparam_t const *xpp, xdfenv_t *env,
+		    struct region *lcs,
+		    int line1, int count1, int line2, int count2)
+{
+	int b_ptr;
+	int sz, ret = -1;
+	struct histindex index;
+
+	memset(&index, 0, sizeof(index));
+
+	index.env = env;
+	index.xpp = xpp;
+
+	index.records = NULL;
+	index.line_map = NULL;
+	/* in case of early xdl_cha_free() */
+	index.rcha.head = NULL;
+
+	index.table_bits = xdl_hashbits(count1);
+	sz = index.records_size = 1 << index.table_bits;
+	sz *= sizeof(struct record *);
+	if (!(index.records = (struct record **) xdl_malloc(sz)))
+		goto cleanup;
+	memset(index.records, 0, sz);
+
+	sz = index.line_map_size = count1;
+	sz *= sizeof(struct record *);
+	if (!(index.line_map = (struct record **) xdl_malloc(sz)))
+		goto cleanup;
+	memset(index.line_map, 0, sz);
+
+	sz = index.line_map_size;
+	sz *= sizeof(unsigned int);
+	if (!(index.next_ptrs = (unsigned int *) xdl_malloc(sz)))
+		goto cleanup;
+	memset(index.next_ptrs, 0, sz);
+
+	/* lines / 4 + 1 comes from xprepare.c:xdl_prepare_ctx() */
+	if (xdl_cha_init(&index.rcha, sizeof(struct record), count1 / 4 + 1) < 0)
+		goto cleanup;
+
+	index.ptr_shift = line1;
+	index.max_chain_length = 64;
+
+	if (scanA(&index, line1, count1))
+		goto cleanup;
+
+	index.cnt = index.max_chain_length + 1;
+
+	for (b_ptr = line2; b_ptr <= LINE_END(2); )
+		b_ptr = try_lcs(&index, lcs, b_ptr, line1, count1, line2, count2);
+
+	if (index.has_common && index.max_chain_length < index.cnt)
+		ret = 1;
+	else
+		ret = 0;
+
+cleanup:
+	free_index(&index);
+	return ret;
+}
+
+static int histogram_diff(xpparam_t const *xpp, xdfenv_t *env,
+	int line1, int count1, int line2, int count2)
+{
+	struct region lcs;
+	int lcs_found;
+	int result;
+redo:
+	result = -1;
+
+	if (count1 <= 0 && count2 <= 0)
+		return 0;
+
+	if (LINE_END(1) >= MAX_PTR)
+		return -1;
+
+	if (!count1) {
+		while(count2--)
+			env->xdf2.rchg[line2++ - 1] = 1;
+		return 0;
+	} else if (!count2) {
+		while(count1--)
+			env->xdf1.rchg[line1++ - 1] = 1;
+		return 0;
+	}
+
+	memset(&lcs, 0, sizeof(lcs));
+	lcs_found = find_lcs(xpp, env, &lcs, line1, count1, line2, count2);
+	if (lcs_found < 0)
+		goto out;
+	else if (lcs_found)
+		result = fall_back_to_classic_diff(xpp, env, line1, count1, line2, count2);
+	else {
+		if (lcs.begin1 == 0 && lcs.begin2 == 0) {
+			while (count1--)
+				env->xdf1.rchg[line1++ - 1] = 1;
+			while (count2--)
+				env->xdf2.rchg[line2++ - 1] = 1;
+			result = 0;
+		} else {
+			result = histogram_diff(xpp, env,
+						line1, lcs.begin1 - line1,
+						line2, lcs.begin2 - line2);
+			if (result)
+				goto out;
+			/*
+			 * result = histogram_diff(xpp, env,
+			 *            lcs.end1 + 1, LINE_END(1) - lcs.end1,
+			 *            lcs.end2 + 1, LINE_END(2) - lcs.end2);
+			 * but let's optimize tail recursion ourself:
+			*/
+			count1 = LINE_END(1) - lcs.end1;
+			line1 = lcs.end1 + 1;
+			count2 = LINE_END(2) - lcs.end2;
+			line2 = lcs.end2 + 1;
+			goto redo;
+		}
+	}
+out:
+	return result;
+}
+
+int xdl_do_histogram_diff(mmfile_t *file1, mmfile_t *file2,
+	xpparam_t const *xpp, xdfenv_t *env)
+{
+	if (xdl_prepare_env(file1, file2, xpp, env) < 0)
+		return -1;
+
+	return histogram_diff(xpp, env,
+		env->xdf1.dstart + 1, env->xdf1.dend - env->xdf1.dstart + 1,
+		env->xdf2.dstart + 1, env->xdf2.dend - env->xdf2.dstart + 1);
+}
diff --git a/src/xdiff/xinclude.h b/src/xdiff/xinclude.h
new file mode 100644
index 0000000..46b8608
--- /dev/null
+++ b/src/xdiff/xinclude.h
@@ -0,0 +1,61 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003  Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+/* defines HAVE_ATTRIBUTE_UNUSED */
+#ifdef HAVE_CONFIG_H
+# include "../auto/config.h"
+#endif
+
+/* Mark unused function arguments with UNUSED, so that gcc -Wunused-parameter
+ * can be used to check for mistakes. */
+#ifdef HAVE_ATTRIBUTE_UNUSED
+# define UNUSED __attribute__((unused))
+#else
+# define UNUSED
+#endif
+
+#if defined(_MSC_VER)
+# define inline __inline
+#endif
+
+#if !defined(XINCLUDE_H)
+#define XINCLUDE_H
+
+#include <ctype.h>
+#include <stdio.h>
+#include <stdlib.h>
+#if !defined(_WIN32)
+#include <unistd.h>
+#endif
+#include <string.h>
+#include <limits.h>
+
+#include "xmacros.h"
+#include "xdiff.h"
+#include "xtypes.h"
+#include "xutils.h"
+#include "xprepare.h"
+#include "xdiffi.h"
+#include "xemit.h"
+
+
+#endif /* #if !defined(XINCLUDE_H) */
diff --git a/src/xdiff/xmacros.h b/src/xdiff/xmacros.h
new file mode 100644
index 0000000..2809a28
--- /dev/null
+++ b/src/xdiff/xmacros.h
@@ -0,0 +1,54 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003  Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#if !defined(XMACROS_H)
+#define XMACROS_H
+
+
+
+
+#define XDL_MIN(a, b) ((a) < (b) ? (a): (b))
+#define XDL_MAX(a, b) ((a) > (b) ? (a): (b))
+#define XDL_ABS(v) ((v) >= 0 ? (v): -(v))
+#define XDL_ISDIGIT(c) ((c) >= '0' && (c) <= '9')
+#define XDL_ISSPACE(c) (isspace((unsigned char)(c)))
+#define XDL_ADDBITS(v,b)	((v) + ((v) >> (b)))
+#define XDL_MASKBITS(b)		((1UL << (b)) - 1)
+#define XDL_HASHLONG(v,b)	(XDL_ADDBITS((unsigned long)(v), b) & XDL_MASKBITS(b))
+#define XDL_PTRFREE(p) do { if (p) { xdl_free(p); (p) = NULL; } } while (0)
+#define XDL_LE32_PUT(p, v) \
+do { \
+	unsigned char *__p = (unsigned char *) (p); \
+	*__p++ = (unsigned char) (v); \
+	*__p++ = (unsigned char) ((v) >> 8); \
+	*__p++ = (unsigned char) ((v) >> 16); \
+	*__p = (unsigned char) ((v) >> 24); \
+} while (0)
+#define XDL_LE32_GET(p, v) \
+do { \
+	unsigned char const *__p = (unsigned char const *) (p); \
+	(v) = (unsigned long) __p[0] | ((unsigned long) __p[1]) << 8 | \
+		((unsigned long) __p[2]) << 16 | ((unsigned long) __p[3]) << 24; \
+} while (0)
+
+
+#endif /* #if !defined(XMACROS_H) */
diff --git a/src/xdiff/xpatience.c b/src/xdiff/xpatience.c
new file mode 100644
index 0000000..1052d10
--- /dev/null
+++ b/src/xdiff/xpatience.c
@@ -0,0 +1,390 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003-2016 Davide Libenzi, Johannes E. Schindelin
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+#include "xinclude.h"
+#include "xtypes.h"
+#include "xdiff.h"
+
+/*
+ * The basic idea of patience diff is to find lines that are unique in
+ * both files.  These are intuitively the ones that we want to see as
+ * common lines.
+ *
+ * The maximal ordered sequence of such line pairs (where ordered means
+ * that the order in the sequence agrees with the order of the lines in
+ * both files) naturally defines an initial set of common lines.
+ *
+ * Now, the algorithm tries to extend the set of common lines by growing
+ * the line ranges where the files have identical lines.
+ *
+ * Between those common lines, the patience diff algorithm is applied
+ * recursively, until no unique line pairs can be found; these line ranges
+ * are handled by the well-known Myers algorithm.
+ */
+
+#define NON_UNIQUE ULONG_MAX
+
+/*
+ * This is a hash mapping from line hash to line numbers in the first and
+ * second file.
+ */
+struct hashmap {
+	int nr, alloc;
+	struct entry {
+		unsigned long hash;
+		/*
+		 * 0 = unused entry, 1 = first line, 2 = second, etc.
+		 * line2 is NON_UNIQUE if the line is not unique
+		 * in either the first or the second file.
+		 */
+		unsigned long line1, line2;
+		/*
+		 * "next" & "previous" are used for the longest common
+		 * sequence;
+		 * initially, "next" reflects only the order in file1.
+		 */
+		struct entry *next, *previous;
+
+		/*
+		 * If 1, this entry can serve as an anchor. See
+		 * Documentation/diff-options.txt for more information.
+		 */
+		unsigned anchor : 1;
+	} *entries, *first, *last;
+	/* were common records found? */
+	unsigned long has_matches;
+	mmfile_t *file1, *file2;
+	xdfenv_t *env;
+	xpparam_t const *xpp;
+};
+
+static int is_anchor(xpparam_t const *xpp, const char *line)
+{
+	size_t i;
+	for (i = 0; i < xpp->anchors_nr; i++) {
+		if (!strncmp(line, xpp->anchors[i], strlen(xpp->anchors[i])))
+			return 1;
+	}
+	return 0;
+}
+
+/* The argument "pass" is 1 for the first file, 2 for the second. */
+static void insert_record(xpparam_t const *xpp, int line, struct hashmap *map,
+			  int pass)
+{
+	xrecord_t **records = pass == 1 ?
+		map->env->xdf1.recs : map->env->xdf2.recs;
+	xrecord_t *record = records[line - 1], *other;
+	/*
+	 * After xdl_prepare_env() (or more precisely, due to
+	 * xdl_classify_record()), the "ha" member of the records (AKA lines)
+	 * is _not_ the hash anymore, but a linearized version of it.  In
+	 * other words, the "ha" member is guaranteed to start with 0 and
+	 * the second record's ha can only be 0 or 1, etc.
+	 *
+	 * So we multiply ha by 2 in the hope that the hashing was
+	 * "unique enough".
+	 */
+	int index = (int)((record->ha << 1) % map->alloc);
+
+	while (map->entries[index].line1) {
+		other = map->env->xdf1.recs[map->entries[index].line1 - 1];
+		if (map->entries[index].hash != record->ha ||
+				!xdl_recmatch(record->ptr, record->size,
+					other->ptr, other->size,
+					map->xpp->flags)) {
+			if (++index >= map->alloc)
+				index = 0;
+			continue;
+		}
+		if (pass == 2)
+			map->has_matches = 1;
+		if (pass == 1 || map->entries[index].line2)
+			map->entries[index].line2 = NON_UNIQUE;
+		else
+			map->entries[index].line2 = line;
+		return;
+	}
+	if (pass == 2)
+		return;
+	map->entries[index].line1 = line;
+	map->entries[index].hash = record->ha;
+	map->entries[index].anchor = is_anchor(xpp, map->env->xdf1.recs[line - 1]->ptr);
+	if (!map->first)
+		map->first = map->entries + index;
+	if (map->last) {
+		map->last->next = map->entries + index;
+		map->entries[index].previous = map->last;
+	}
+	map->last = map->entries + index;
+	map->nr++;
+}
+
+/*
+ * This function has to be called for each recursion into the inter-hunk
+ * parts, as previously non-unique lines can become unique when being
+ * restricted to a smaller part of the files.
+ *
+ * It is assumed that env has been prepared using xdl_prepare().
+ */
+static int fill_hashmap(mmfile_t *file1, mmfile_t *file2,
+		xpparam_t const *xpp, xdfenv_t *env,
+		struct hashmap *result,
+		int line1, int count1, int line2, int count2)
+{
+	result->file1 = file1;
+	result->file2 = file2;
+	result->xpp = xpp;
+	result->env = env;
+
+	/* We know exactly how large we want the hash map */
+	result->alloc = count1 * 2;
+	result->entries = (struct entry *)
+		xdl_malloc(result->alloc * sizeof(struct entry));
+	if (!result->entries)
+		return -1;
+	memset(result->entries, 0, result->alloc * sizeof(struct entry));
+
+	/* First, fill with entries from the first file */
+	while (count1--)
+		insert_record(xpp, line1++, result, 1);
+
+	/* Then search for matches in the second file */
+	while (count2--)
+		insert_record(xpp, line2++, result, 2);
+
+	return 0;
+}
+
+/*
+ * Find the longest sequence with a smaller last element (meaning a smaller
+ * line2, as we construct the sequence with entries ordered by line1).
+ */
+static int binary_search(struct entry **sequence, int longest,
+		struct entry *entry)
+{
+	int left = -1, right = longest;
+
+	while (left + 1 < right) {
+		int middle = left + (right - left) / 2;
+		/* by construction, no two entries can be equal */
+		if (sequence[middle]->line2 > entry->line2)
+			right = middle;
+		else
+			left = middle;
+	}
+	/* return the index in "sequence", _not_ the sequence length */
+	return left;
+}
+
+/*
+ * The idea is to start with the list of common unique lines sorted by
+ * the order in file1.  For each of these pairs, the longest (partial)
+ * sequence whose last element's line2 is smaller is determined.
+ *
+ * For efficiency, the sequences are kept in a list containing exactly one
+ * item per sequence length: the sequence with the smallest last
+ * element (in terms of line2).
+ */
+static struct entry *find_longest_common_sequence(struct hashmap *map)
+{
+	struct entry **sequence = xdl_malloc(map->nr * sizeof(struct entry *));
+	int longest = 0, i;
+	struct entry *entry;
+
+	/*
+	 * If not -1, this entry in sequence must never be overridden.
+	 * Therefore, overriding entries before this has no effect, so
+	 * do not do that either.
+	 */
+	int anchor_i = -1;
+
+	for (entry = map->first; entry; entry = entry->next) {
+		if (!entry->line2 || entry->line2 == NON_UNIQUE)
+			continue;
+		i = binary_search(sequence, longest, entry);
+		entry->previous = i < 0 ? NULL : sequence[i];
+		++i;
+		if (i <= anchor_i)
+			continue;
+		sequence[i] = entry;
+		if (entry->anchor) {
+			anchor_i = i;
+			longest = anchor_i + 1;
+		} else if (i == longest) {
+			longest++;
+		}
+	}
+
+	/* No common unique lines were found */
+	if (!longest) {
+		xdl_free(sequence);
+		return NULL;
+	}
+
+	/* Iterate starting at the last element, adjusting the "next" members */
+	entry = sequence[longest - 1];
+	entry->next = NULL;
+	while (entry->previous) {
+		entry->previous->next = entry;
+		entry = entry->previous;
+	}
+	xdl_free(sequence);
+	return entry;
+}
+
+static int match(struct hashmap *map, int line1, int line2)
+{
+	xrecord_t *record1 = map->env->xdf1.recs[line1 - 1];
+	xrecord_t *record2 = map->env->xdf2.recs[line2 - 1];
+	return xdl_recmatch(record1->ptr, record1->size,
+		record2->ptr, record2->size, map->xpp->flags);
+}
+
+static int patience_diff(mmfile_t *file1, mmfile_t *file2,
+		xpparam_t const *xpp, xdfenv_t *env,
+		int line1, int count1, int line2, int count2);
+
+static int walk_common_sequence(struct hashmap *map, struct entry *first,
+		int line1, int count1, int line2, int count2)
+{
+	int end1 = line1 + count1, end2 = line2 + count2;
+	int next1, next2;
+
+	for (;;) {
+		/* Try to grow the line ranges of common lines */
+		if (first) {
+			next1 = first->line1;
+			next2 = first->line2;
+			while (next1 > line1 && next2 > line2 &&
+					match(map, next1 - 1, next2 - 1)) {
+				next1--;
+				next2--;
+			}
+		} else {
+			next1 = end1;
+			next2 = end2;
+		}
+		while (line1 < next1 && line2 < next2 &&
+				match(map, line1, line2)) {
+			line1++;
+			line2++;
+		}
+
+		/* Recurse */
+		if (next1 > line1 || next2 > line2) {
+			struct hashmap submap;
+
+			memset(&submap, 0, sizeof(submap));
+			if (patience_diff(map->file1, map->file2,
+					map->xpp, map->env,
+					line1, next1 - line1,
+					line2, next2 - line2))
+				return -1;
+		}
+
+		if (!first)
+			return 0;
+
+		while (first->next &&
+				first->next->line1 == first->line1 + 1 &&
+				first->next->line2 == first->line2 + 1)
+			first = first->next;
+
+		line1 = first->line1 + 1;
+		line2 = first->line2 + 1;
+
+		first = first->next;
+	}
+}
+
+static int fall_back_to_classic_diff(struct hashmap *map,
+		int line1, int count1, int line2, int count2)
+{
+	xpparam_t xpp;
+	xpp.flags = map->xpp->flags & ~XDF_DIFF_ALGORITHM_MASK;
+
+	return xdl_fall_back_diff(map->env, &xpp,
+				  line1, count1, line2, count2);
+}
+
+/*
+ * Recursively find the longest common sequence of unique lines,
+ * and if none was found, ask xdl_do_diff() to do the job.
+ *
+ * This function assumes that env was prepared with xdl_prepare_env().
+ */
+static int patience_diff(mmfile_t *file1, mmfile_t *file2,
+		xpparam_t const *xpp, xdfenv_t *env,
+		int line1, int count1, int line2, int count2)
+{
+	struct hashmap map;
+	struct entry *first;
+	int result = 0;
+
+	/* trivial case: one side is empty */
+	if (!count1) {
+		while(count2--)
+			env->xdf2.rchg[line2++ - 1] = 1;
+		return 0;
+	} else if (!count2) {
+		while(count1--)
+			env->xdf1.rchg[line1++ - 1] = 1;
+		return 0;
+	}
+
+	memset(&map, 0, sizeof(map));
+	if (fill_hashmap(file1, file2, xpp, env, &map,
+			line1, count1, line2, count2))
+		return -1;
+
+	/* are there any matching lines at all? */
+	if (!map.has_matches) {
+		while(count1--)
+			env->xdf1.rchg[line1++ - 1] = 1;
+		while(count2--)
+			env->xdf2.rchg[line2++ - 1] = 1;
+		xdl_free(map.entries);
+		return 0;
+	}
+
+	first = find_longest_common_sequence(&map);
+	if (first)
+		result = walk_common_sequence(&map, first,
+			line1, count1, line2, count2);
+	else
+		result = fall_back_to_classic_diff(&map,
+			line1, count1, line2, count2);
+
+	xdl_free(map.entries);
+	return result;
+}
+
+int xdl_do_patience_diff(mmfile_t *file1, mmfile_t *file2,
+		xpparam_t const *xpp, xdfenv_t *env)
+{
+	if (xdl_prepare_env(file1, file2, xpp, env) < 0)
+		return -1;
+
+	/* environment is cleaned up in xdl_diff() */
+	return patience_diff(file1, file2, xpp, env,
+			1, env->xdf1.nrec, 1, env->xdf2.nrec);
+}
diff --git a/src/xdiff/xprepare.c b/src/xdiff/xprepare.c
new file mode 100644
index 0000000..abeb8fb
--- /dev/null
+++ b/src/xdiff/xprepare.c
@@ -0,0 +1,483 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003  Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#include "xinclude.h"
+
+
+#define XDL_KPDIS_RUN 4
+#define XDL_MAX_EQLIMIT 1024
+#define XDL_SIMSCAN_WINDOW 100
+#define XDL_GUESS_NLINES1 256
+#define XDL_GUESS_NLINES2 20
+
+
+typedef struct s_xdlclass {
+	struct s_xdlclass *next;
+	unsigned long ha;
+	char const *line;
+	long size;
+	long idx;
+	long len1, len2;
+} xdlclass_t;
+
+typedef struct s_xdlclassifier {
+	unsigned int hbits;
+	long hsize;
+	xdlclass_t **rchash;
+	chastore_t ncha;
+	xdlclass_t **rcrecs;
+	long alloc;
+	long count;
+	long flags;
+} xdlclassifier_t;
+
+
+
+
+static int xdl_init_classifier(xdlclassifier_t *cf, long size, long flags);
+static void xdl_free_classifier(xdlclassifier_t *cf);
+static int xdl_classify_record(unsigned int pass, xdlclassifier_t *cf, xrecord_t **rhash,
+			       unsigned int hbits, xrecord_t *rec);
+static int xdl_prepare_ctx(unsigned int pass, mmfile_t *mf, long narec, xpparam_t const *xpp,
+			   xdlclassifier_t *cf, xdfile_t *xdf);
+static void xdl_free_ctx(xdfile_t *xdf);
+static int xdl_clean_mmatch(char const *dis, long i, long s, long e);
+static int xdl_cleanup_records(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xdf2);
+static int xdl_trim_ends(xdfile_t *xdf1, xdfile_t *xdf2);
+static int xdl_optimize_ctxs(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xdf2);
+
+
+
+
+static int xdl_init_classifier(xdlclassifier_t *cf, long size, long flags) {
+	cf->flags = flags;
+
+	cf->hbits = xdl_hashbits((unsigned int) size);
+	cf->hsize = 1 << cf->hbits;
+
+	if (xdl_cha_init(&cf->ncha, sizeof(xdlclass_t), size / 4 + 1) < 0) {
+
+		return -1;
+	}
+	if (!(cf->rchash = (xdlclass_t **) xdl_malloc(cf->hsize * sizeof(xdlclass_t *)))) {
+
+		xdl_cha_free(&cf->ncha);
+		return -1;
+	}
+	memset(cf->rchash, 0, cf->hsize * sizeof(xdlclass_t *));
+
+	cf->alloc = size;
+	if (!(cf->rcrecs = (xdlclass_t **) xdl_malloc(cf->alloc * sizeof(xdlclass_t *)))) {
+
+		xdl_free(cf->rchash);
+		xdl_cha_free(&cf->ncha);
+		return -1;
+	}
+
+	cf->count = 0;
+
+	return 0;
+}
+
+
+static void xdl_free_classifier(xdlclassifier_t *cf) {
+
+	xdl_free(cf->rcrecs);
+	xdl_free(cf->rchash);
+	xdl_cha_free(&cf->ncha);
+}
+
+
+static int xdl_classify_record(unsigned int pass, xdlclassifier_t *cf, xrecord_t **rhash,
+			       unsigned int hbits, xrecord_t *rec) {
+	long hi;
+	char const *line;
+	xdlclass_t *rcrec;
+	xdlclass_t **rcrecs;
+
+	line = rec->ptr;
+	hi = (long) XDL_HASHLONG(rec->ha, cf->hbits);
+	for (rcrec = cf->rchash[hi]; rcrec; rcrec = rcrec->next)
+		if (rcrec->ha == rec->ha &&
+				xdl_recmatch(rcrec->line, rcrec->size,
+					rec->ptr, rec->size, cf->flags))
+			break;
+
+	if (!rcrec) {
+		if (!(rcrec = xdl_cha_alloc(&cf->ncha))) {
+
+			return -1;
+		}
+		rcrec->idx = cf->count++;
+		if (cf->count > cf->alloc) {
+			cf->alloc *= 2;
+			if (!(rcrecs = (xdlclass_t **) xdl_realloc(cf->rcrecs, cf->alloc * sizeof(xdlclass_t *)))) {
+
+				return -1;
+			}
+			cf->rcrecs = rcrecs;
+		}
+		cf->rcrecs[rcrec->idx] = rcrec;
+		rcrec->line = line;
+		rcrec->size = rec->size;
+		rcrec->ha = rec->ha;
+		rcrec->len1 = rcrec->len2 = 0;
+		rcrec->next = cf->rchash[hi];
+		cf->rchash[hi] = rcrec;
+	}
+
+	(pass == 1) ? rcrec->len1++ : rcrec->len2++;
+
+	rec->ha = (unsigned long) rcrec->idx;
+
+	hi = (long) XDL_HASHLONG(rec->ha, hbits);
+	rec->next = rhash[hi];
+	rhash[hi] = rec;
+
+	return 0;
+}
+
+
+static int xdl_prepare_ctx(unsigned int pass, mmfile_t *mf, long narec, xpparam_t const *xpp,
+			   xdlclassifier_t *cf, xdfile_t *xdf) {
+	unsigned int hbits;
+	long nrec, hsize, bsize;
+	unsigned long hav;
+	char const *blk, *cur, *top, *prev;
+	xrecord_t *crec;
+	xrecord_t **recs, **rrecs;
+	xrecord_t **rhash;
+	unsigned long *ha;
+	char *rchg;
+	long *rindex;
+
+	ha = NULL;
+	rindex = NULL;
+	rchg = NULL;
+	rhash = NULL;
+	recs = NULL;
+
+	if (xdl_cha_init(&xdf->rcha, sizeof(xrecord_t), narec / 4 + 1) < 0)
+		goto abort;
+	if (!(recs = (xrecord_t **) xdl_malloc(narec * sizeof(xrecord_t *))))
+		goto abort;
+
+	if (XDF_DIFF_ALG(xpp->flags) == XDF_HISTOGRAM_DIFF)
+		hbits = hsize = 0;
+	else {
+		hbits = xdl_hashbits((unsigned int) narec);
+		hsize = 1 << hbits;
+		if (!(rhash = (xrecord_t **) xdl_malloc(hsize * sizeof(xrecord_t *))))
+			goto abort;
+		memset(rhash, 0, hsize * sizeof(xrecord_t *));
+	}
+
+	nrec = 0;
+	if ((cur = blk = xdl_mmfile_first(mf, &bsize)) != NULL) {
+		for (top = blk + bsize; cur < top; ) {
+			prev = cur;
+			hav = xdl_hash_record(&cur, top, xpp->flags);
+			if (nrec >= narec) {
+				narec *= 2;
+				if (!(rrecs = (xrecord_t **) xdl_realloc(recs, narec * sizeof(xrecord_t *))))
+					goto abort;
+				recs = rrecs;
+			}
+			if (!(crec = xdl_cha_alloc(&xdf->rcha)))
+				goto abort;
+			crec->ptr = prev;
+			crec->size = (long) (cur - prev);
+			crec->ha = hav;
+			recs[nrec++] = crec;
+
+			if ((XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF) &&
+			    xdl_classify_record(pass, cf, rhash, hbits, crec) < 0)
+				goto abort;
+		}
+	}
+
+	if (!(rchg = (char *) xdl_malloc((nrec + 2) * sizeof(char))))
+		goto abort;
+	memset(rchg, 0, (nrec + 2) * sizeof(char));
+
+	if (!(rindex = (long *) xdl_malloc((nrec + 1) * sizeof(long))))
+		goto abort;
+	if (!(ha = (unsigned long *) xdl_malloc((nrec + 1) * sizeof(unsigned long))))
+		goto abort;
+
+	xdf->nrec = nrec;
+	xdf->recs = recs;
+	xdf->hbits = hbits;
+	xdf->rhash = rhash;
+	xdf->rchg = rchg + 1;
+	xdf->rindex = rindex;
+	xdf->nreff = 0;
+	xdf->ha = ha;
+	xdf->dstart = 0;
+	xdf->dend = nrec - 1;
+
+	return 0;
+
+abort:
+	xdl_free(ha);
+	xdl_free(rindex);
+	xdl_free(rchg);
+	xdl_free(rhash);
+	xdl_free(recs);
+	xdl_cha_free(&xdf->rcha);
+	return -1;
+}
+
+
+static void xdl_free_ctx(xdfile_t *xdf) {
+
+	xdl_free(xdf->rhash);
+	xdl_free(xdf->rindex);
+	xdl_free(xdf->rchg - 1);
+	xdl_free(xdf->ha);
+	xdl_free(xdf->recs);
+	xdl_cha_free(&xdf->rcha);
+}
+
+
+int xdl_prepare_env(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
+		    xdfenv_t *xe) {
+	long enl1, enl2, sample;
+	xdlclassifier_t cf;
+
+	memset(&cf, 0, sizeof(cf));
+
+	/*
+	 * For histogram diff, we can afford a smaller sample size and
+	 * thus a poorer estimate of the number of lines, as the hash
+	 * table (rhash) won't be filled up/grown. The number of lines
+	 * (nrecs) will be updated correctly anyway by
+	 * xdl_prepare_ctx().
+	 */
+	sample = (XDF_DIFF_ALG(xpp->flags) == XDF_HISTOGRAM_DIFF
+		  ? XDL_GUESS_NLINES2 : XDL_GUESS_NLINES1);
+
+	enl1 = xdl_guess_lines(mf1, sample) + 1;
+	enl2 = xdl_guess_lines(mf2, sample) + 1;
+
+	if (XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF &&
+	    xdl_init_classifier(&cf, enl1 + enl2 + 1, xpp->flags) < 0)
+		return -1;
+
+	if (xdl_prepare_ctx(1, mf1, enl1, xpp, &cf, &xe->xdf1) < 0) {
+
+		xdl_free_classifier(&cf);
+		return -1;
+	}
+	if (xdl_prepare_ctx(2, mf2, enl2, xpp, &cf, &xe->xdf2) < 0) {
+
+		xdl_free_ctx(&xe->xdf1);
+		xdl_free_classifier(&cf);
+		return -1;
+	}
+
+	if ((XDF_DIFF_ALG(xpp->flags) != XDF_PATIENCE_DIFF) &&
+	    (XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF) &&
+	    xdl_optimize_ctxs(&cf, &xe->xdf1, &xe->xdf2) < 0) {
+
+		xdl_free_ctx(&xe->xdf2);
+		xdl_free_ctx(&xe->xdf1);
+		xdl_free_classifier(&cf);
+		return -1;
+	}
+
+	if (XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF)
+		xdl_free_classifier(&cf);
+
+	return 0;
+}
+
+
+void xdl_free_env(xdfenv_t *xe) {
+
+	xdl_free_ctx(&xe->xdf2);
+	xdl_free_ctx(&xe->xdf1);
+}
+
+
+static int xdl_clean_mmatch(char const *dis, long i, long s, long e) {
+	long r, rdis0, rpdis0, rdis1, rpdis1;
+
+	/*
+	 * Limits the window the is examined during the similar-lines
+	 * scan. The loops below stops when dis[i - r] == 1 (line that
+	 * has no match), but there are corner cases where the loop
+	 * proceed all the way to the extremities by causing huge
+	 * performance penalties in case of big files.
+	 */
+	if (i - s > XDL_SIMSCAN_WINDOW)
+		s = i - XDL_SIMSCAN_WINDOW;
+	if (e - i > XDL_SIMSCAN_WINDOW)
+		e = i + XDL_SIMSCAN_WINDOW;
+
+	/*
+	 * Scans the lines before 'i' to find a run of lines that either
+	 * have no match (dis[j] == 0) or have multiple matches (dis[j] > 1).
+	 * Note that we always call this function with dis[i] > 1, so the
+	 * current line (i) is already a multimatch line.
+	 */
+	for (r = 1, rdis0 = 0, rpdis0 = 1; (i - r) >= s; r++) {
+		if (!dis[i - r])
+			rdis0++;
+		else if (dis[i - r] == 2)
+			rpdis0++;
+		else
+			break;
+	}
+	/*
+	 * If the run before the line 'i' found only multimatch lines, we
+	 * return 0 and hence we don't make the current line (i) discarded.
+	 * We want to discard multimatch lines only when they appear in the
+	 * middle of runs with nomatch lines (dis[j] == 0).
+	 */
+	if (rdis0 == 0)
+		return 0;
+	for (r = 1, rdis1 = 0, rpdis1 = 1; (i + r) <= e; r++) {
+		if (!dis[i + r])
+			rdis1++;
+		else if (dis[i + r] == 2)
+			rpdis1++;
+		else
+			break;
+	}
+	/*
+	 * If the run after the line 'i' found only multimatch lines, we
+	 * return 0 and hence we don't make the current line (i) discarded.
+	 */
+	if (rdis1 == 0)
+		return 0;
+	rdis1 += rdis0;
+	rpdis1 += rpdis0;
+
+	return rpdis1 * XDL_KPDIS_RUN < (rpdis1 + rdis1);
+}
+
+
+/*
+ * Try to reduce the problem complexity, discard records that have no
+ * matches on the other file. Also, lines that have multiple matches
+ * might be potentially discarded if they happear in a run of discardable.
+ */
+static int xdl_cleanup_records(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xdf2) {
+	long i, nm, nreff, mlim;
+	xrecord_t **recs;
+	xdlclass_t *rcrec;
+	char *dis, *dis1, *dis2;
+
+	if (!(dis = (char *) xdl_malloc(xdf1->nrec + xdf2->nrec + 2))) {
+
+		return -1;
+	}
+	memset(dis, 0, xdf1->nrec + xdf2->nrec + 2);
+	dis1 = dis;
+	dis2 = dis1 + xdf1->nrec + 1;
+
+	if ((mlim = xdl_bogosqrt(xdf1->nrec)) > XDL_MAX_EQLIMIT)
+		mlim = XDL_MAX_EQLIMIT;
+	for (i = xdf1->dstart, recs = &xdf1->recs[xdf1->dstart]; i <= xdf1->dend; i++, recs++) {
+		rcrec = cf->rcrecs[(*recs)->ha];
+		nm = rcrec ? rcrec->len2 : 0;
+		dis1[i] = (nm == 0) ? 0: (nm >= mlim) ? 2: 1;
+	}
+
+	if ((mlim = xdl_bogosqrt(xdf2->nrec)) > XDL_MAX_EQLIMIT)
+		mlim = XDL_MAX_EQLIMIT;
+	for (i = xdf2->dstart, recs = &xdf2->recs[xdf2->dstart]; i <= xdf2->dend; i++, recs++) {
+		rcrec = cf->rcrecs[(*recs)->ha];
+		nm = rcrec ? rcrec->len1 : 0;
+		dis2[i] = (nm == 0) ? 0: (nm >= mlim) ? 2: 1;
+	}
+
+	for (nreff = 0, i = xdf1->dstart, recs = &xdf1->recs[xdf1->dstart];
+	     i <= xdf1->dend; i++, recs++) {
+		if (dis1[i] == 1 ||
+		    (dis1[i] == 2 && !xdl_clean_mmatch(dis1, i, xdf1->dstart, xdf1->dend))) {
+			xdf1->rindex[nreff] = i;
+			xdf1->ha[nreff] = (*recs)->ha;
+			nreff++;
+		} else
+			xdf1->rchg[i] = 1;
+	}
+	xdf1->nreff = nreff;
+
+	for (nreff = 0, i = xdf2->dstart, recs = &xdf2->recs[xdf2->dstart];
+	     i <= xdf2->dend; i++, recs++) {
+		if (dis2[i] == 1 ||
+		    (dis2[i] == 2 && !xdl_clean_mmatch(dis2, i, xdf2->dstart, xdf2->dend))) {
+			xdf2->rindex[nreff] = i;
+			xdf2->ha[nreff] = (*recs)->ha;
+			nreff++;
+		} else
+			xdf2->rchg[i] = 1;
+	}
+	xdf2->nreff = nreff;
+
+	xdl_free(dis);
+
+	return 0;
+}
+
+
+/*
+ * Early trim initial and terminal matching records.
+ */
+static int xdl_trim_ends(xdfile_t *xdf1, xdfile_t *xdf2) {
+	long i, lim;
+	xrecord_t **recs1, **recs2;
+
+	recs1 = xdf1->recs;
+	recs2 = xdf2->recs;
+	for (i = 0, lim = XDL_MIN(xdf1->nrec, xdf2->nrec); i < lim;
+	     i++, recs1++, recs2++)
+		if ((*recs1)->ha != (*recs2)->ha)
+			break;
+
+	xdf1->dstart = xdf2->dstart = i;
+
+	recs1 = xdf1->recs + xdf1->nrec - 1;
+	recs2 = xdf2->recs + xdf2->nrec - 1;
+	for (lim -= i, i = 0; i < lim; i++, recs1--, recs2--)
+		if ((*recs1)->ha != (*recs2)->ha)
+			break;
+
+	xdf1->dend = xdf1->nrec - i - 1;
+	xdf2->dend = xdf2->nrec - i - 1;
+
+	return 0;
+}
+
+
+static int xdl_optimize_ctxs(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xdf2) {
+
+	if (xdl_trim_ends(xdf1, xdf2) < 0 ||
+	    xdl_cleanup_records(cf, xdf1, xdf2) < 0) {
+
+		return -1;
+	}
+
+	return 0;
+}
diff --git a/src/xdiff/xprepare.h b/src/xdiff/xprepare.h
new file mode 100644
index 0000000..947d9fc
--- /dev/null
+++ b/src/xdiff/xprepare.h
@@ -0,0 +1,34 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003  Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#if !defined(XPREPARE_H)
+#define XPREPARE_H
+
+
+
+int xdl_prepare_env(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
+		    xdfenv_t *xe);
+void xdl_free_env(xdfenv_t *xe);
+
+
+
+#endif /* #if !defined(XPREPARE_H) */
diff --git a/src/xdiff/xtypes.h b/src/xdiff/xtypes.h
new file mode 100644
index 0000000..8442bd4
--- /dev/null
+++ b/src/xdiff/xtypes.h
@@ -0,0 +1,67 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003  Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#if !defined(XTYPES_H)
+#define XTYPES_H
+
+
+
+typedef struct s_chanode {
+	struct s_chanode *next;
+	long icurr;
+} chanode_t;
+
+typedef struct s_chastore {
+	chanode_t *head, *tail;
+	long isize, nsize;
+	chanode_t *ancur;
+	chanode_t *sncur;
+	long scurr;
+} chastore_t;
+
+typedef struct s_xrecord {
+	struct s_xrecord *next;
+	char const *ptr;
+	long size;
+	unsigned long ha;
+} xrecord_t;
+
+typedef struct s_xdfile {
+	chastore_t rcha;
+	long nrec;
+	unsigned int hbits;
+	xrecord_t **rhash;
+	long dstart, dend;
+	xrecord_t **recs;
+	char *rchg;
+	long *rindex;
+	long nreff;
+	unsigned long *ha;
+} xdfile_t;
+
+typedef struct s_xdfenv {
+	xdfile_t xdf1, xdf2;
+} xdfenv_t;
+
+
+
+#endif /* #if !defined(XTYPES_H) */
diff --git a/src/xdiff/xutils.c b/src/xdiff/xutils.c
new file mode 100644
index 0000000..4ab6ca8
--- /dev/null
+++ b/src/xdiff/xutils.c
@@ -0,0 +1,425 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003	Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#include <limits.h>
+#include <assert.h>
+#include "xinclude.h"
+
+
+
+
+long xdl_bogosqrt(long n) {
+	long i;
+
+	/*
+	 * Classical integer square root approximation using shifts.
+	 */
+	for (i = 1; n > 0; n >>= 2)
+		i <<= 1;
+
+	return i;
+}
+
+
+int xdl_emit_diffrec(char const *rec, long size, char const *pre, long psize,
+		     xdemitcb_t *ecb) {
+	int i = 2;
+	mmbuffer_t mb[3];
+
+	mb[0].ptr = (char *) pre;
+	mb[0].size = psize;
+	mb[1].ptr = (char *) rec;
+	mb[1].size = size;
+	if (size > 0 && rec[size - 1] != '\n') {
+		mb[2].ptr = (char *) "\n\\ No newline at end of file\n";
+		mb[2].size = strlen(mb[2].ptr);
+		i++;
+	}
+	if (ecb->outf(ecb->priv, mb, i) < 0) {
+
+		return -1;
+	}
+
+	return 0;
+}
+
+void *xdl_mmfile_first(mmfile_t *mmf, long *size)
+{
+	*size = mmf->size;
+	return mmf->ptr;
+}
+
+
+long xdl_mmfile_size(mmfile_t *mmf)
+{
+	return mmf->size;
+}
+
+
+int xdl_cha_init(chastore_t *cha, long isize, long icount) {
+
+	cha->head = cha->tail = NULL;
+	cha->isize = isize;
+	cha->nsize = icount * isize;
+	cha->ancur = cha->sncur = NULL;
+	cha->scurr = 0;
+
+	return 0;
+}
+
+
+void xdl_cha_free(chastore_t *cha) {
+	chanode_t *cur, *tmp;
+
+	for (cur = cha->head; (tmp = cur) != NULL;) {
+		cur = cur->next;
+		xdl_free(tmp);
+	}
+}
+
+
+void *xdl_cha_alloc(chastore_t *cha) {
+	chanode_t *ancur;
+	void *data;
+
+	if (!(ancur = cha->ancur) || ancur->icurr == cha->nsize) {
+		if (!(ancur = (chanode_t *) xdl_malloc(sizeof(chanode_t) + cha->nsize))) {
+
+			return NULL;
+		}
+		ancur->icurr = 0;
+		ancur->next = NULL;
+		if (cha->tail)
+			cha->tail->next = ancur;
+		if (!cha->head)
+			cha->head = ancur;
+		cha->tail = ancur;
+		cha->ancur = ancur;
+	}
+
+	data = (char *) ancur + sizeof(chanode_t) + ancur->icurr;
+	ancur->icurr += cha->isize;
+
+	return data;
+}
+
+long xdl_guess_lines(mmfile_t *mf, long sample) {
+	long nl = 0, size, tsize = 0;
+	char const *data, *cur, *top;
+
+	if ((cur = data = xdl_mmfile_first(mf, &size)) != NULL) {
+		for (top = data + size; nl < sample && cur < top; ) {
+			nl++;
+			if (!(cur = memchr(cur, '\n', top - cur)))
+				cur = top;
+			else
+				cur++;
+		}
+		tsize += (long) (cur - data);
+	}
+
+	if (nl && tsize)
+		nl = xdl_mmfile_size(mf) / (tsize / nl);
+
+	return nl + 1;
+}
+
+int xdl_blankline(const char *line, long size, long flags)
+{
+	long i;
+
+	if (!(flags & XDF_WHITESPACE_FLAGS))
+		return (size <= 1);
+
+	for (i = 0; i < size && XDL_ISSPACE(line[i]); i++)
+		;
+
+	return (i == size);
+}
+
+/*
+ * Have we eaten everything on the line, except for an optional
+ * CR at the very end?
+ */
+static int ends_with_optional_cr(const char *l, long s, long i)
+{
+	int complete = s && l[s-1] == '\n';
+
+	if (complete)
+		s--;
+	if (s == i)
+		return 1;
+	/* do not ignore CR at the end of an incomplete line */
+	if (complete && s == i + 1 && l[i] == '\r')
+		return 1;
+	return 0;
+}
+
+int xdl_recmatch(const char *l1, long s1, const char *l2, long s2, long flags)
+{
+	int i1, i2;
+
+	if (s1 == s2 && !memcmp(l1, l2, s1))
+		return 1;
+	if (!(flags & XDF_WHITESPACE_FLAGS))
+		return 0;
+
+	i1 = 0;
+	i2 = 0;
+
+	/*
+	 * -w matches everything that matches with -b, and -b in turn
+	 * matches everything that matches with --ignore-space-at-eol,
+	 * which in turn matches everything that matches with --ignore-cr-at-eol.
+	 *
+	 * Each flavor of ignoring needs different logic to skip whitespaces
+	 * while we have both sides to compare.
+	 */
+	if (flags & XDF_IGNORE_WHITESPACE) {
+		goto skip_ws;
+		while (i1 < s1 && i2 < s2) {
+			if (l1[i1++] != l2[i2++])
+				return 0;
+		skip_ws:
+			while (i1 < s1 && XDL_ISSPACE(l1[i1]))
+				i1++;
+			while (i2 < s2 && XDL_ISSPACE(l2[i2]))
+				i2++;
+		}
+	} else if (flags & XDF_IGNORE_WHITESPACE_CHANGE) {
+		while (i1 < s1 && i2 < s2) {
+			if (XDL_ISSPACE(l1[i1]) && XDL_ISSPACE(l2[i2])) {
+				/* Skip matching spaces and try again */
+				while (i1 < s1 && XDL_ISSPACE(l1[i1]))
+					i1++;
+				while (i2 < s2 && XDL_ISSPACE(l2[i2]))
+					i2++;
+				continue;
+			}
+			if (l1[i1++] != l2[i2++])
+				return 0;
+		}
+	} else if (flags & XDF_IGNORE_WHITESPACE_AT_EOL) {
+		while (i1 < s1 && i2 < s2 && l1[i1] == l2[i2]) {
+			i1++;
+			i2++;
+		}
+	} else if (flags & XDF_IGNORE_CR_AT_EOL) {
+		/* Find the first difference and see how the line ends */
+		while (i1 < s1 && i2 < s2 && l1[i1] == l2[i2]) {
+			i1++;
+			i2++;
+		}
+		return (ends_with_optional_cr(l1, s1, i1) &&
+			ends_with_optional_cr(l2, s2, i2));
+	}
+
+	/*
+	 * After running out of one side, the remaining side must have
+	 * nothing but whitespace for the lines to match.  Note that
+	 * ignore-whitespace-at-eol case may break out of the loop
+	 * while there still are characters remaining on both lines.
+	 */
+	if (i1 < s1) {
+		while (i1 < s1 && XDL_ISSPACE(l1[i1]))
+			i1++;
+		if (s1 != i1)
+			return 0;
+	}
+	if (i2 < s2) {
+		while (i2 < s2 && XDL_ISSPACE(l2[i2]))
+			i2++;
+		return (s2 == i2);
+	}
+	return 1;
+}
+
+static unsigned long xdl_hash_record_with_whitespace(char const **data,
+		char const *top, long flags) {
+	unsigned long ha = 5381;
+	char const *ptr = *data;
+	int cr_at_eol_only = (flags & XDF_WHITESPACE_FLAGS) == XDF_IGNORE_CR_AT_EOL;
+
+	for (; ptr < top && *ptr != '\n'; ptr++) {
+		if (cr_at_eol_only) {
+			/* do not ignore CR at the end of an incomplete line */
+			if (*ptr == '\r' &&
+			    (ptr + 1 < top && ptr[1] == '\n'))
+				continue;
+		}
+		else if (XDL_ISSPACE(*ptr)) {
+			const char *ptr2 = ptr;
+			int at_eol;
+			while (ptr + 1 < top && XDL_ISSPACE(ptr[1])
+					&& ptr[1] != '\n')
+				ptr++;
+			at_eol = (top <= ptr + 1 || ptr[1] == '\n');
+			if (flags & XDF_IGNORE_WHITESPACE)
+				; /* already handled */
+			else if (flags & XDF_IGNORE_WHITESPACE_CHANGE
+				 && !at_eol) {
+				ha += (ha << 5);
+				ha ^= (unsigned long) ' ';
+			}
+			else if (flags & XDF_IGNORE_WHITESPACE_AT_EOL
+				 && !at_eol) {
+				while (ptr2 != ptr + 1) {
+					ha += (ha << 5);
+					ha ^= (unsigned long) *ptr2;
+					ptr2++;
+				}
+			}
+			continue;
+		}
+		ha += (ha << 5);
+		ha ^= (unsigned long) *ptr;
+	}
+	*data = ptr < top ? ptr + 1: ptr;
+
+	return ha;
+}
+
+unsigned long xdl_hash_record(char const **data, char const *top, long flags) {
+	unsigned long ha = 5381;
+	char const *ptr = *data;
+
+	if (flags & XDF_WHITESPACE_FLAGS)
+		return xdl_hash_record_with_whitespace(data, top, flags);
+
+	for (; ptr < top && *ptr != '\n'; ptr++) {
+		ha += (ha << 5);
+		ha ^= (unsigned long) *ptr;
+	}
+	*data = ptr < top ? ptr + 1: ptr;
+
+	return ha;
+}
+
+unsigned int xdl_hashbits(unsigned int size) {
+	unsigned int val = 1, bits = 0;
+
+	for (; val < size && bits < CHAR_BIT * sizeof(unsigned int); val <<= 1, bits++);
+	return bits ? bits: 1;
+}
+
+
+int xdl_num_out(char *out, long val) {
+	char *ptr, *str = out;
+	char buf[32];
+
+	ptr = buf + sizeof(buf) - 1;
+	*ptr = '\0';
+	if (val < 0) {
+		*--ptr = '-';
+		val = -val;
+	}
+	for (; val && ptr > buf; val /= 10)
+		*--ptr = "0123456789"[val % 10];
+	if (*ptr)
+		for (; *ptr; ptr++, str++)
+			*str = *ptr;
+	else
+		*str++ = '0';
+	*str = '\0';
+
+	return str - out;
+}
+
+int xdl_emit_hunk_hdr(long s1, long c1, long s2, long c2,
+		      const char *func, long funclen, xdemitcb_t *ecb) {
+	int nb = 0;
+	mmbuffer_t mb;
+	char buf[128];
+
+	memcpy(buf, "@@ -", 4);
+	nb += 4;
+
+	nb += xdl_num_out(buf + nb, c1 ? s1: s1 - 1);
+
+	if (c1 != 1) {
+		memcpy(buf + nb, ",", 1);
+		nb += 1;
+
+		nb += xdl_num_out(buf + nb, c1);
+	}
+
+	memcpy(buf + nb, " +", 2);
+	nb += 2;
+
+	nb += xdl_num_out(buf + nb, c2 ? s2: s2 - 1);
+
+	if (c2 != 1) {
+		memcpy(buf + nb, ",", 1);
+		nb += 1;
+
+		nb += xdl_num_out(buf + nb, c2);
+	}
+
+	memcpy(buf + nb, " @@", 3);
+	nb += 3;
+	if (func && funclen) {
+		buf[nb++] = ' ';
+		if (funclen > (long)sizeof(buf) - nb - 1)
+			funclen = sizeof(buf) - nb - 1;
+		memcpy(buf + nb, func, funclen);
+		nb += funclen;
+	}
+	buf[nb++] = '\n';
+
+	mb.ptr = buf;
+	mb.size = nb;
+	if (ecb->outf(ecb->priv, &mb, 1) < 0)
+		return -1;
+
+	return 0;
+}
+
+int xdl_fall_back_diff(xdfenv_t *diff_env, xpparam_t const *xpp,
+		int line1, int count1, int line2, int count2)
+{
+	/*
+	 * This probably does not work outside Git, since
+	 * we have a very simple mmfile structure.
+	 *
+	 * Note: ideally, we would reuse the prepared environment, but
+	 * the libxdiff interface does not (yet) allow for diffing only
+	 * ranges of lines instead of the whole files.
+	 */
+	mmfile_t subfile1, subfile2;
+	xdfenv_t env;
+
+	subfile1.ptr = (char *)diff_env->xdf1.recs[line1 - 1]->ptr;
+	subfile1.size = diff_env->xdf1.recs[line1 + count1 - 2]->ptr +
+		diff_env->xdf1.recs[line1 + count1 - 2]->size - subfile1.ptr;
+	subfile2.ptr = (char *)diff_env->xdf2.recs[line2 - 1]->ptr;
+	subfile2.size = diff_env->xdf2.recs[line2 + count2 - 2]->ptr +
+		diff_env->xdf2.recs[line2 + count2 - 2]->size - subfile2.ptr;
+	if (xdl_do_diff(&subfile1, &subfile2, xpp, &env) < 0)
+		return -1;
+
+	memcpy(diff_env->xdf1.rchg + line1 - 1, env.xdf1.rchg, count1);
+	memcpy(diff_env->xdf2.rchg + line2 - 1, env.xdf2.rchg, count2);
+
+	xdl_free_env(&env);
+
+	return 0;
+}
diff --git a/src/xdiff/xutils.h b/src/xdiff/xutils.h
new file mode 100644
index 0000000..fba7bae
--- /dev/null
+++ b/src/xdiff/xutils.h
@@ -0,0 +1,47 @@
+/*
+ *  LibXDiff by Davide Libenzi ( File Differential Library )
+ *  Copyright (C) 2003  Davide Libenzi
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, see
+ *  <http://www.gnu.org/licenses/>.
+ *
+ *  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#if !defined(XUTILS_H)
+#define XUTILS_H
+
+
+
+long xdl_bogosqrt(long n);
+int xdl_emit_diffrec(char const *rec, long size, char const *pre, long psize,
+		     xdemitcb_t *ecb);
+int xdl_cha_init(chastore_t *cha, long isize, long icount);
+void xdl_cha_free(chastore_t *cha);
+void *xdl_cha_alloc(chastore_t *cha);
+long xdl_guess_lines(mmfile_t *mf, long sample);
+int xdl_blankline(const char *line, long size, long flags);
+int xdl_recmatch(const char *l1, long s1, const char *l2, long s2, long flags);
+unsigned long xdl_hash_record(char const **data, char const *top, long flags);
+unsigned int xdl_hashbits(unsigned int size);
+int xdl_num_out(char *out, long val);
+int xdl_emit_hunk_hdr(long s1, long c1, long s2, long c2,
+		      const char *func, long funclen, xdemitcb_t *ecb);
+int xdl_fall_back_diff(xdfenv_t *diff_env, xpparam_t const *xpp,
+		       int line1, int count1, int line2, int count2);
+
+
+
+#endif /* #if !defined(XUTILS_H) */