diff --git a/src/undo.c b/src/undo.c
new file mode 100644
index 0000000..6efcffa
--- /dev/null
+++ b/src/undo.c
@@ -0,0 +1,1380 @@
+/* vi:set ts=8 sts=4 sw=4:
+ *
+ * VIM - Vi IMproved	by Bram Moolenaar
+ *
+ * Do ":help uganda"  in Vim to read copying and usage conditions.
+ * Do ":help credits" in Vim to see a list of people who contributed.
+ * See README.txt for an overview of the Vim source code.
+ */
+
+/*
+ * undo.c: multi level undo facility
+ *
+ * The saved lines are stored in a list of lists (one for each buffer):
+ *
+ * b_u_oldhead------------------------------------------------+
+ *							      |
+ *							      V
+ *		  +--------------+    +--------------+	  +--------------+
+ * b_u_newhead--->| u_header	 |    | u_header     |	  | u_header	 |
+ *		  |	uh_next------>|     uh_next------>|	uh_next---->NULL
+ *	   NULL<--------uh_prev  |<---------uh_prev  |<---------uh_prev  |
+ *		  |	uh_entry |    |     uh_entry |	  |	uh_entry |
+ *		  +--------|-----+    +--------|-----+	  +--------|-----+
+ *			   |		       |		   |
+ *			   V		       V		   V
+ *		  +--------------+    +--------------+	  +--------------+
+ *		  | u_entry	 |    | u_entry      |	  | u_entry	 |
+ *		  |	ue_next  |    |     ue_next  |	  |	ue_next  |
+ *		  +--------|-----+    +--------|-----+	  +--------|-----+
+ *			   |		       |		   |
+ *			   V		       V		   V
+ *		  +--------------+	      NULL		  NULL
+ *		  | u_entry	 |
+ *		  |	ue_next  |
+ *		  +--------|-----+
+ *			   |
+ *			   V
+ *			  etc.
+ *
+ * Each u_entry list contains the information for one undo or redo.
+ * curbuf->b_u_curhead points to the header of the last undo (the next redo),
+ * or is NULL if nothing has been undone.
+ *
+ * All data is allocated with u_alloc_line(), thus it will be freed as soon as
+ * we switch files!
+ */
+
+#include "vim.h"
+
+static u_entry_T *u_get_headentry __ARGS((void));
+static void u_getbot __ARGS((void));
+static int u_savecommon __ARGS((linenr_T, linenr_T, linenr_T));
+static void u_doit __ARGS((int count));
+static void u_undoredo __ARGS((void));
+static void u_undo_end __ARGS((void));
+static void u_freelist __ARGS((struct u_header *));
+static void u_freeentry __ARGS((u_entry_T *, long));
+
+static char_u *u_blockalloc __ARGS((long_u));
+static void u_free_line __ARGS((char_u *, int keep));
+static char_u *u_alloc_line __ARGS((unsigned));
+static char_u *u_save_line __ARGS((linenr_T));
+
+static long	u_newcount, u_oldcount;
+
+/*
+ * When 'u' flag included in 'cpoptions', we behave like vi.  Need to remember
+ * the action that "u" should do.
+ */
+static int	undo_undoes = FALSE;
+
+/*
+ * save the current line for both the "u" and "U" command
+ */
+    int
+u_save_cursor()
+{
+    return (u_save((linenr_T)(curwin->w_cursor.lnum - 1),
+				      (linenr_T)(curwin->w_cursor.lnum + 1)));
+}
+
+/*
+ * Save the lines between "top" and "bot" for both the "u" and "U" command.
+ * "top" may be 0 and bot may be curbuf->b_ml.ml_line_count + 1.
+ * Returns FAIL when lines could not be saved, OK otherwise.
+ */
+    int
+u_save(top, bot)
+    linenr_T top, bot;
+{
+    if (undo_off)
+	return OK;
+
+    if (top > curbuf->b_ml.ml_line_count ||
+			    top >= bot || bot > curbuf->b_ml.ml_line_count + 1)
+	return FALSE;	/* rely on caller to do error messages */
+
+    if (top + 2 == bot)
+	u_saveline((linenr_T)(top + 1));
+
+    return (u_savecommon(top, bot, (linenr_T)0));
+}
+
+/*
+ * save the line "lnum" (used by ":s" and "~" command)
+ * The line is replaced, so the new bottom line is lnum + 1.
+ */
+    int
+u_savesub(lnum)
+    linenr_T	lnum;
+{
+    if (undo_off)
+	return OK;
+
+    return (u_savecommon(lnum - 1, lnum + 1, lnum + 1));
+}
+
+/*
+ * a new line is inserted before line "lnum" (used by :s command)
+ * The line is inserted, so the new bottom line is lnum + 1.
+ */
+    int
+u_inssub(lnum)
+    linenr_T	lnum;
+{
+    if (undo_off)
+	return OK;
+
+    return (u_savecommon(lnum - 1, lnum, lnum + 1));
+}
+
+/*
+ * save the lines "lnum" - "lnum" + nlines (used by delete command)
+ * The lines are deleted, so the new bottom line is lnum, unless the buffer
+ * becomes empty.
+ */
+    int
+u_savedel(lnum, nlines)
+    linenr_T	lnum;
+    long	nlines;
+{
+    if (undo_off)
+	return OK;
+
+    return (u_savecommon(lnum - 1, lnum + nlines,
+			nlines == curbuf->b_ml.ml_line_count ? 2 : lnum));
+}
+
+    static int
+u_savecommon(top, bot, newbot)
+    linenr_T	top, bot;
+    linenr_T	newbot;
+{
+    linenr_T		lnum;
+    long		i;
+    struct u_header	*uhp;
+    u_entry_T		*uep;
+    u_entry_T		*prev_uep;
+    long		size;
+
+    /*
+     * Don't allow changes when 'modifiable' is off.  Letting the
+     * undo fail is a crude way to make all change commands fail.
+     */
+    if (!curbuf->b_p_ma)
+    {
+	EMSG(_(e_modifiable));
+	return FAIL;
+    }
+
+#ifdef HAVE_SANDBOX
+    /*
+     * In the sandbox it's not allowed to change the text.  Letting the
+     * undo fail is a crude way to make all change commands fail.
+     */
+    if (sandbox != 0)
+    {
+	EMSG(_(e_sandbox));
+	return FAIL;
+    }
+#endif
+
+#ifdef FEAT_NETBEANS_INTG
+    /*
+     * Netbeans defines areas that cannot be modified.  Bail out here when
+     * trying to change text in a guarded area.
+     */
+    if (usingNetbeans && netbeans_is_guarded(top, bot))
+    {
+	EMSG(_(e_guarded));
+	return FAIL;
+    }
+#endif
+
+#ifdef FEAT_AUTOCMD
+    /*
+     * Saving text for undo means we are going to make a change.  Give a
+     * warning for a read-only file before making the change, so that the
+     * FileChangedRO event can replace the buffer with a read-write version
+     * (e.g., obtained from a source control system).
+     */
+    change_warning(0);
+#endif
+
+    size = bot - top - 1;
+
+    /*
+     * if curbuf->b_u_synced == TRUE make a new header
+     */
+    if (curbuf->b_u_synced)
+    {
+#ifdef FEAT_JUMPLIST
+	/* Need to create new entry in b_changelist. */
+	curbuf->b_new_change = TRUE;
+#endif
+
+	/*
+	 * if we undid more than we redid, free the entry lists before and
+	 * including curbuf->b_u_curhead
+	 */
+	while (curbuf->b_u_curhead != NULL)
+	    u_freelist(curbuf->b_u_newhead);
+
+	/*
+	 * free headers to keep the size right
+	 */
+	while (curbuf->b_u_numhead > p_ul && curbuf->b_u_oldhead != NULL)
+	    u_freelist(curbuf->b_u_oldhead);
+
+	if (p_ul < 0)		/* no undo at all */
+	{
+	    curbuf->b_u_synced = FALSE;
+	    return OK;
+	}
+
+	/*
+	 * make a new header entry
+	 */
+	uhp = (struct u_header *)u_alloc_line((unsigned)
+						     sizeof(struct u_header));
+	if (uhp == NULL)
+	    goto nomem;
+	uhp->uh_prev = NULL;
+	uhp->uh_next = curbuf->b_u_newhead;
+	if (curbuf->b_u_newhead != NULL)
+	    curbuf->b_u_newhead->uh_prev = uhp;
+	uhp->uh_entry = NULL;
+	uhp->uh_getbot_entry = NULL;
+	uhp->uh_cursor = curwin->w_cursor;	/* save cursor pos. for undo */
+#ifdef FEAT_VIRTUALEDIT
+	if (virtual_active() && curwin->w_cursor.coladd > 0)
+	    uhp->uh_cursor_vcol = getviscol();
+	else
+	    uhp->uh_cursor_vcol = -1;
+#endif
+
+	/* save changed and buffer empty flag for undo */
+	uhp->uh_flags = (curbuf->b_changed ? UH_CHANGED : 0) +
+		       ((curbuf->b_ml.ml_flags & ML_EMPTY) ? UH_EMPTYBUF : 0);
+
+	/* save named marks for undo */
+	mch_memmove(uhp->uh_namedm, curbuf->b_namedm, sizeof(pos_T) * NMARKS);
+	curbuf->b_u_newhead = uhp;
+	if (curbuf->b_u_oldhead == NULL)
+	    curbuf->b_u_oldhead = uhp;
+	++curbuf->b_u_numhead;
+    }
+    else
+    {
+	if (p_ul < 0)		/* no undo at all */
+	    return OK;
+
+	/*
+	 * When saving a single line, and it has been saved just before, it
+	 * doesn't make sense saving it again.  Saves a lot of memory when
+	 * making lots of changes inside the same line.
+	 * This is only possible if the previous change didn't increase or
+	 * decrease the number of lines.
+	 * Check the ten last changes.  More doesn't make sense and takes too
+	 * long.
+	 */
+	if (size == 1)
+	{
+	    uep = u_get_headentry();
+	    prev_uep = NULL;
+	    for (i = 0; i < 10; ++i)
+	    {
+		if (uep == NULL)
+		    break;
+
+		/* If lines have been inserted/deleted we give up.
+		 * Also when the line was included in a multi-line save. */
+		if ((curbuf->b_u_newhead->uh_getbot_entry != uep
+			    ? (uep->ue_top + uep->ue_size + 1
+				!= (uep->ue_bot == 0
+				    ? curbuf->b_ml.ml_line_count + 1
+				    : uep->ue_bot))
+			    : uep->ue_lcount != curbuf->b_ml.ml_line_count)
+			|| (uep->ue_size > 1
+			    && top >= uep->ue_top
+			    && top + 2 <= uep->ue_top + uep->ue_size + 1))
+		    break;
+
+		/* If it's the same line we can skip saving it again. */
+		if (uep->ue_size == 1 && uep->ue_top == top)
+		{
+		    if (i > 0)
+		    {
+			/* It's not the last entry: get ue_bot for the last
+			 * entry now.  Following deleted/inserted lines go to
+			 * the re-used entry. */
+			u_getbot();
+			curbuf->b_u_synced = FALSE;
+
+			/* Move the found entry to become the last entry.  The
+			 * order of undo/redo doesn't matter for the entries
+			 * we move it over, since they don't change the line
+			 * count and don't include this line.  It does matter
+			 * for the found entry if the line count is changed by
+			 * the executed command. */
+			prev_uep->ue_next = uep->ue_next;
+			uep->ue_next = curbuf->b_u_newhead->uh_entry;
+			curbuf->b_u_newhead->uh_entry = uep;
+		    }
+
+		    /* The executed command may change the line count. */
+		    if (newbot != 0)
+			uep->ue_bot = newbot;
+		    else if (bot > curbuf->b_ml.ml_line_count)
+			uep->ue_bot = 0;
+		    else
+		    {
+			uep->ue_lcount = curbuf->b_ml.ml_line_count;
+			curbuf->b_u_newhead->uh_getbot_entry = uep;
+		    }
+		    return OK;
+		}
+		prev_uep = uep;
+		uep = uep->ue_next;
+	    }
+	}
+
+	/* find line number for ue_bot for previous u_save() */
+	u_getbot();
+    }
+
+#if !defined(UNIX) && !defined(DJGPP) && !defined(WIN32) && !defined(__EMX__)
+	/*
+	 * With Amiga and MSDOS 16 bit we can't handle big undo's, because
+	 * then u_alloc_line would have to allocate a block larger than 32K
+	 */
+    if (size >= 8000)
+	goto nomem;
+#endif
+
+    /*
+     * add lines in front of entry list
+     */
+    uep = (u_entry_T *)u_alloc_line((unsigned)sizeof(u_entry_T));
+    if (uep == NULL)
+	goto nomem;
+
+    uep->ue_size = size;
+    uep->ue_top = top;
+    if (newbot != 0)
+	uep->ue_bot = newbot;
+    /*
+     * Use 0 for ue_bot if bot is below last line.
+     * Otherwise we have to compute ue_bot later.
+     */
+    else if (bot > curbuf->b_ml.ml_line_count)
+	uep->ue_bot = 0;
+    else
+    {
+	uep->ue_lcount = curbuf->b_ml.ml_line_count;
+	curbuf->b_u_newhead->uh_getbot_entry = uep;
+    }
+
+    if (size)
+    {
+	if ((uep->ue_array = (char_u **)u_alloc_line(
+				(unsigned)(sizeof(char_u *) * size))) == NULL)
+	{
+	    u_freeentry(uep, 0L);
+	    goto nomem;
+	}
+	for (i = 0, lnum = top + 1; i < size; ++i)
+	{
+	    if ((uep->ue_array[i] = u_save_line(lnum++)) == NULL)
+	    {
+		u_freeentry(uep, i);
+		goto nomem;
+	    }
+	}
+    }
+    uep->ue_next = curbuf->b_u_newhead->uh_entry;
+    curbuf->b_u_newhead->uh_entry = uep;
+    curbuf->b_u_synced = FALSE;
+    undo_undoes = FALSE;
+
+    return OK;
+
+nomem:
+    msg_silent = 0;	/* must display the prompt */
+    if (ask_yesno((char_u *)_("No undo possible; continue anyway"), TRUE)
+								       == 'y')
+    {
+	undo_off = TRUE;	    /* will be reset when character typed */
+	return OK;
+    }
+    do_outofmem_msg((long_u)0);
+    return FAIL;
+}
+
+/*
+ * If 'cpoptions' contains 'u': Undo the previous undo or redo (vi compatible).
+ * If 'cpoptions' does not contain 'u': Always undo.
+ */
+    void
+u_undo(count)
+    int count;
+{
+    /*
+     * If we get an undo command while executing a macro, we behave like the
+     * original vi. If this happens twice in one macro the result will not
+     * be compatible.
+     */
+    if (curbuf->b_u_synced == FALSE)
+    {
+	u_sync();
+	count = 1;
+    }
+
+    if (vim_strchr(p_cpo, CPO_UNDO) == NULL)
+	undo_undoes = TRUE;
+    else
+	undo_undoes = !undo_undoes;
+    u_doit(count);
+}
+
+/*
+ * If 'cpoptions' contains 'u': Repeat the previous undo or redo.
+ * If 'cpoptions' does not contain 'u': Always redo.
+ */
+    void
+u_redo(count)
+    int count;
+{
+    if (vim_strchr(p_cpo, CPO_UNDO) == NULL)
+	undo_undoes = FALSE;
+    u_doit(count);
+}
+
+/*
+ * Undo or redo, depending on 'undo_undoes', 'count' times.
+ */
+    static void
+u_doit(count)
+    int count;
+{
+    /* Don't allow changes when 'modifiable' is off. */
+    if (!curbuf->b_p_ma)
+    {
+	EMSG(_(e_modifiable));
+	return;
+    }
+#ifdef HAVE_SANDBOX
+    /* In the sandbox it's not allowed to change the text. */
+    if (sandbox != 0)
+    {
+	EMSG(_(e_sandbox));
+	return;
+    }
+#endif
+
+    u_newcount = 0;
+    u_oldcount = 0;
+    while (count--)
+    {
+	if (undo_undoes)
+	{
+	    if (curbuf->b_u_curhead == NULL)		/* first undo */
+		curbuf->b_u_curhead = curbuf->b_u_newhead;
+	    else if (p_ul > 0)				/* multi level undo */
+		/* get next undo */
+		curbuf->b_u_curhead = curbuf->b_u_curhead->uh_next;
+	    /* nothing to undo */
+	    if (curbuf->b_u_numhead == 0 || curbuf->b_u_curhead == NULL)
+	    {
+		/* stick curbuf->b_u_curhead at end */
+		curbuf->b_u_curhead = curbuf->b_u_oldhead;
+		beep_flush();
+		break;
+	    }
+
+	    u_undoredo();
+	}
+	else
+	{
+	    if (curbuf->b_u_curhead == NULL || p_ul <= 0)
+	    {
+		beep_flush();	/* nothing to redo */
+		break;
+	    }
+
+	    u_undoredo();
+	    /* advance for next redo */
+	    curbuf->b_u_curhead = curbuf->b_u_curhead->uh_prev;
+	}
+    }
+    u_undo_end();
+}
+
+/*
+ * u_undoredo: common code for undo and redo
+ *
+ * The lines in the file are replaced by the lines in the entry list at
+ * curbuf->b_u_curhead. The replaced lines in the file are saved in the entry
+ * list for the next undo/redo.
+ */
+    static void
+u_undoredo()
+{
+    char_u	**newarray = NULL;
+    linenr_T	oldsize;
+    linenr_T	newsize;
+    linenr_T	top, bot;
+    linenr_T	lnum;
+    linenr_T	newlnum = MAXLNUM;
+    long	i;
+    u_entry_T	*uep, *nuep;
+    u_entry_T	*newlist = NULL;
+    int		old_flags;
+    int		new_flags;
+    pos_T	namedm[NMARKS];
+    int		empty_buffer;		    /* buffer became empty */
+
+    old_flags = curbuf->b_u_curhead->uh_flags;
+    new_flags = (curbuf->b_changed ? UH_CHANGED : 0) +
+	       ((curbuf->b_ml.ml_flags & ML_EMPTY) ? UH_EMPTYBUF : 0);
+    setpcmark();
+
+    /*
+     * save marks before undo/redo
+     */
+    mch_memmove(namedm, curbuf->b_namedm, sizeof(pos_T) * NMARKS);
+    curbuf->b_op_start.lnum = curbuf->b_ml.ml_line_count;
+    curbuf->b_op_start.col = 0;
+    curbuf->b_op_end.lnum = 0;
+    curbuf->b_op_end.col = 0;
+
+    for (uep = curbuf->b_u_curhead->uh_entry; uep != NULL; uep = nuep)
+    {
+	top = uep->ue_top;
+	bot = uep->ue_bot;
+	if (bot == 0)
+	    bot = curbuf->b_ml.ml_line_count + 1;
+	if (top > curbuf->b_ml.ml_line_count || top >= bot
+				      || bot > curbuf->b_ml.ml_line_count + 1)
+	{
+	    EMSG(_("E438: u_undo: line numbers wrong"));
+	    changed();		/* don't want UNCHANGED now */
+	    return;
+	}
+
+	oldsize = bot - top - 1;    /* number of lines before undo */
+	newsize = uep->ue_size;	    /* number of lines after undo */
+
+	if (top < newlnum)
+	{
+	    /* If the saved cursor is somewhere in this undo block, move it to
+	     * the remembered position.  Makes "gwap" put the cursor back
+	     * where it was. */
+	    lnum = curbuf->b_u_curhead->uh_cursor.lnum;
+	    if (lnum >= top && lnum <= top + newsize + 1)
+	    {
+		curwin->w_cursor = curbuf->b_u_curhead->uh_cursor;
+		newlnum = curwin->w_cursor.lnum - 1;
+	    }
+	    else
+	    {
+		/* Use the first line that actually changed.  Avoids that
+		 * undoing auto-formatting puts the cursor in the previous
+		 * line. */
+		for (i = 0; i < newsize && i < oldsize; ++i)
+		    if (STRCMP(uep->ue_array[i], ml_get(top + 1 + i)) != 0)
+			break;
+		if (i == newsize && newlnum == MAXLNUM && uep->ue_next == NULL)
+		{
+		    newlnum = top;
+		    curwin->w_cursor.lnum = newlnum + 1;
+		}
+		else if (i < newsize)
+		{
+		    newlnum = top + i;
+		    curwin->w_cursor.lnum = newlnum + 1;
+		}
+	    }
+	}
+
+	empty_buffer = FALSE;
+
+	/* delete the lines between top and bot and save them in newarray */
+	if (oldsize)
+	{
+	    if ((newarray = (char_u **)u_alloc_line(
+			    (unsigned)(sizeof(char_u *) * oldsize))) == NULL)
+	    {
+		do_outofmem_msg((long_u)(sizeof(char_u *) * oldsize));
+		/*
+		 * We have messed up the entry list, repair is impossible.
+		 * we have to free the rest of the list.
+		 */
+		while (uep != NULL)
+		{
+		    nuep = uep->ue_next;
+		    u_freeentry(uep, uep->ue_size);
+		    uep = nuep;
+		}
+		break;
+	    }
+	    /* delete backwards, it goes faster in most cases */
+	    for (lnum = bot - 1, i = oldsize; --i >= 0; --lnum)
+	    {
+		/* what can we do when we run out of memory? */
+		if ((newarray[i] = u_save_line(lnum)) == NULL)
+		    do_outofmem_msg((long_u)0);
+		/* remember we deleted the last line in the buffer, and a
+		 * dummy empty line will be inserted */
+		if (curbuf->b_ml.ml_line_count == 1)
+		    empty_buffer = TRUE;
+		ml_delete(lnum, FALSE);
+	    }
+	}
+
+	/* insert the lines in u_array between top and bot */
+	if (newsize)
+	{
+	    for (lnum = top, i = 0; i < newsize; ++i, ++lnum)
+	    {
+		/*
+		 * If the file is empty, there is an empty line 1 that we
+		 * should get rid of, by replacing it with the new line
+		 */
+		if (empty_buffer && lnum == 0)
+		    ml_replace((linenr_T)1, uep->ue_array[i], TRUE);
+		else
+		    ml_append(lnum, uep->ue_array[i], (colnr_T)0, FALSE);
+		u_free_line(uep->ue_array[i], FALSE);
+	    }
+	    u_free_line((char_u *)uep->ue_array, FALSE);
+	}
+
+	/* adjust marks */
+	if (oldsize != newsize)
+	{
+	    mark_adjust(top + 1, top + oldsize, (long)MAXLNUM,
+					       (long)newsize - (long)oldsize);
+	    if (curbuf->b_op_start.lnum > top + oldsize)
+		curbuf->b_op_start.lnum += newsize - oldsize;
+	    if (curbuf->b_op_end.lnum > top + oldsize)
+		curbuf->b_op_end.lnum += newsize - oldsize;
+	}
+
+	changed_lines(top + 1, 0, bot, newsize - oldsize);
+
+	/* set '[ and '] mark */
+	if (top + 1 < curbuf->b_op_start.lnum)
+	    curbuf->b_op_start.lnum = top + 1;
+	if (newsize == 0 && top + 1 > curbuf->b_op_end.lnum)
+	    curbuf->b_op_end.lnum = top + 1;
+	else if (top + newsize > curbuf->b_op_end.lnum)
+	    curbuf->b_op_end.lnum = top + newsize;
+
+	u_newcount += newsize;
+	u_oldcount += oldsize;
+	uep->ue_size = oldsize;
+	uep->ue_array = newarray;
+	uep->ue_bot = top + newsize + 1;
+
+	/*
+	 * insert this entry in front of the new entry list
+	 */
+	nuep = uep->ue_next;
+	uep->ue_next = newlist;
+	newlist = uep;
+    }
+
+    curbuf->b_u_curhead->uh_entry = newlist;
+    curbuf->b_u_curhead->uh_flags = new_flags;
+    if ((old_flags & UH_EMPTYBUF) && bufempty())
+	curbuf->b_ml.ml_flags |= ML_EMPTY;
+    if (old_flags & UH_CHANGED)
+	changed();
+    else
+	unchanged(curbuf, FALSE);
+
+    /*
+     * restore marks from before undo/redo
+     */
+    for (i = 0; i < NMARKS; ++i)
+	if (curbuf->b_u_curhead->uh_namedm[i].lnum)
+	{
+	    curbuf->b_namedm[i] = curbuf->b_u_curhead->uh_namedm[i];
+	    curbuf->b_u_curhead->uh_namedm[i] = namedm[i];
+	}
+
+    /*
+     * If the cursor is only off by one line, put it at the same position as
+     * before starting the change (for the "o" command).
+     * Otherwise the cursor should go to the first undone line.
+     */
+    if (curbuf->b_u_curhead->uh_cursor.lnum + 1 == curwin->w_cursor.lnum
+						 && curwin->w_cursor.lnum > 1)
+	--curwin->w_cursor.lnum;
+    if (curbuf->b_u_curhead->uh_cursor.lnum == curwin->w_cursor.lnum)
+    {
+	curwin->w_cursor.col = curbuf->b_u_curhead->uh_cursor.col;
+#ifdef FEAT_VIRTUALEDIT
+	if (virtual_active() && curbuf->b_u_curhead->uh_cursor_vcol >= 0)
+	    coladvance((colnr_T)curbuf->b_u_curhead->uh_cursor_vcol);
+	else
+	    curwin->w_cursor.coladd = 0;
+#endif
+    }
+    else if (curwin->w_cursor.lnum <= curbuf->b_ml.ml_line_count)
+	beginline(BL_SOL | BL_FIX);
+    else
+    {
+	/* We get here with the current cursor line being past the end (eg
+	 * after adding lines at the end of the file, and then undoing it).
+	 * check_cursor() will move the cursor to the last line.  Move it to
+	 * the first column here. */
+	curwin->w_cursor.col = 0;
+#ifdef FEAT_VIRTUALEDIT
+	curwin->w_cursor.coladd = 0;
+#endif
+    }
+
+    /* Make sure the cursor is on an existing line and column. */
+    check_cursor();
+}
+
+/*
+ * If we deleted or added lines, report the number of less/more lines.
+ * Otherwise, report the number of changes (this may be incorrect
+ * in some cases, but it's better than nothing).
+ */
+    static void
+u_undo_end()
+{
+    if ((u_oldcount -= u_newcount) != 0)
+	msgmore(-u_oldcount);
+    else if (u_newcount > p_report)
+    {
+	if (u_newcount == 1)
+	    MSG(_("1 change"));
+	else
+	    smsg((char_u *)_("%ld changes"), u_newcount);
+    }
+#ifdef FEAT_FOLDING
+    if ((fdo_flags & FDO_UNDO) && KeyTyped)
+	foldOpenCursor();
+#endif
+}
+
+/*
+ * u_sync: stop adding to the current entry list
+ */
+    void
+u_sync()
+{
+    if (curbuf->b_u_synced)
+	return;		    /* already synced */
+#if defined(FEAT_XIM) && defined(FEAT_GUI_GTK)
+    if (im_is_preediting())
+	return;		    /* XIM is busy, don't break an undo sequence */
+#endif
+    if (p_ul < 0)
+	curbuf->b_u_synced = TRUE;  /* no entries, nothing to do */
+    else
+    {
+	u_getbot();		    /* compute ue_bot of previous u_save */
+	curbuf->b_u_curhead = NULL;
+    }
+}
+
+/*
+ * Called after writing the file and setting b_changed to FALSE.
+ * Now an undo means that the buffer is modified.
+ */
+    void
+u_unchanged(buf)
+    buf_T	*buf;
+{
+    struct u_header	*uh;
+
+    for (uh = buf->b_u_newhead; uh; uh = uh->uh_next)
+	uh->uh_flags |= UH_CHANGED;
+    buf->b_did_warn = FALSE;
+}
+
+/*
+ * Get pointer to last added entry.
+ * If it's not valid, give an error message and return NULL.
+ */
+    static u_entry_T *
+u_get_headentry()
+{
+    if (curbuf->b_u_newhead == NULL || curbuf->b_u_newhead->uh_entry == NULL)
+    {
+	EMSG(_("E439: undo list corrupt"));
+	return NULL;
+    }
+    return curbuf->b_u_newhead->uh_entry;
+}
+
+/*
+ * u_getbot(): compute the line number of the previous u_save
+ *		It is called only when b_u_synced is FALSE.
+ */
+    static void
+u_getbot()
+{
+    u_entry_T	*uep;
+    linenr_T	extra;
+
+    uep = u_get_headentry();	/* check for corrupt undo list */
+    if (uep == NULL)
+	return;
+
+    uep = curbuf->b_u_newhead->uh_getbot_entry;
+    if (uep != NULL)
+    {
+	/*
+	 * the new ue_bot is computed from the number of lines that has been
+	 * inserted (0 - deleted) since calling u_save. This is equal to the
+	 * old line count subtracted from the current line count.
+	 */
+	extra = curbuf->b_ml.ml_line_count - uep->ue_lcount;
+	uep->ue_bot = uep->ue_top + uep->ue_size + 1 + extra;
+	if (uep->ue_bot < 1 || uep->ue_bot > curbuf->b_ml.ml_line_count)
+	{
+	    EMSG(_("E440: undo line missing"));
+	    uep->ue_bot = uep->ue_top + 1;  /* assume all lines deleted, will
+					     * get all the old lines back
+					     * without deleting the current
+					     * ones */
+	}
+
+	curbuf->b_u_newhead->uh_getbot_entry = NULL;
+    }
+
+    curbuf->b_u_synced = TRUE;
+}
+
+/*
+ * u_freelist: free one entry list and adjust the pointers
+ */
+    static void
+u_freelist(uhp)
+    struct u_header *uhp;
+{
+    u_entry_T	*uep, *nuep;
+
+    for (uep = uhp->uh_entry; uep != NULL; uep = nuep)
+    {
+	nuep = uep->ue_next;
+	u_freeentry(uep, uep->ue_size);
+    }
+
+    if (curbuf->b_u_curhead == uhp)
+	curbuf->b_u_curhead = NULL;
+
+    if (uhp->uh_next == NULL)
+	curbuf->b_u_oldhead = uhp->uh_prev;
+    else
+	uhp->uh_next->uh_prev = uhp->uh_prev;
+
+    if (uhp->uh_prev == NULL)
+	curbuf->b_u_newhead = uhp->uh_next;
+    else
+	uhp->uh_prev->uh_next = uhp->uh_next;
+
+    u_free_line((char_u *)uhp, FALSE);
+    --curbuf->b_u_numhead;
+}
+
+/*
+ * free entry 'uep' and 'n' lines in uep->ue_array[]
+ */
+    static void
+u_freeentry(uep, n)
+    u_entry_T	*uep;
+    long	    n;
+{
+    while (n)
+	u_free_line(uep->ue_array[--n], FALSE);
+    u_free_line((char_u *)uep, FALSE);
+}
+
+/*
+ * invalidate the undo buffer; called when storage has already been released
+ */
+    void
+u_clearall(buf)
+    buf_T	*buf;
+{
+    buf->b_u_newhead = buf->b_u_oldhead = buf->b_u_curhead = NULL;
+    buf->b_u_synced = TRUE;
+    buf->b_u_numhead = 0;
+    buf->b_u_line_ptr = NULL;
+    buf->b_u_line_lnum = 0;
+}
+
+/*
+ * save the line "lnum" for the "U" command
+ */
+    void
+u_saveline(lnum)
+    linenr_T lnum;
+{
+    if (lnum == curbuf->b_u_line_lnum)	    /* line is already saved */
+	return;
+    if (lnum < 1 || lnum > curbuf->b_ml.ml_line_count)	/* should never happen */
+	return;
+    u_clearline();
+    curbuf->b_u_line_lnum = lnum;
+    if (curwin->w_cursor.lnum == lnum)
+	curbuf->b_u_line_colnr = curwin->w_cursor.col;
+    else
+	curbuf->b_u_line_colnr = 0;
+    if ((curbuf->b_u_line_ptr = u_save_line(lnum)) == NULL)
+	do_outofmem_msg((long_u)0);
+}
+
+/*
+ * clear the line saved for the "U" command
+ * (this is used externally for crossing a line while in insert mode)
+ */
+    void
+u_clearline()
+{
+    if (curbuf->b_u_line_ptr != NULL)
+    {
+	u_free_line(curbuf->b_u_line_ptr, FALSE);
+	curbuf->b_u_line_ptr = NULL;
+	curbuf->b_u_line_lnum = 0;
+    }
+}
+
+/*
+ * Implementation of the "U" command.
+ * Differentiation from vi: "U" can be undone with the next "U".
+ * We also allow the cursor to be in another line.
+ */
+    void
+u_undoline()
+{
+    colnr_T t;
+    char_u  *oldp;
+
+    if (undo_off)
+	return;
+
+    if (curbuf->b_u_line_ptr == NULL ||
+			curbuf->b_u_line_lnum > curbuf->b_ml.ml_line_count)
+    {
+	beep_flush();
+	return;
+    }
+	/* first save the line for the 'u' command */
+    if (u_savecommon(curbuf->b_u_line_lnum - 1,
+				curbuf->b_u_line_lnum + 1, (linenr_T)0) == FAIL)
+	return;
+    oldp = u_save_line(curbuf->b_u_line_lnum);
+    if (oldp == NULL)
+    {
+	do_outofmem_msg((long_u)0);
+	return;
+    }
+    ml_replace(curbuf->b_u_line_lnum, curbuf->b_u_line_ptr, TRUE);
+    changed_bytes(curbuf->b_u_line_lnum, 0);
+    u_free_line(curbuf->b_u_line_ptr, FALSE);
+    curbuf->b_u_line_ptr = oldp;
+
+    t = curbuf->b_u_line_colnr;
+    if (curwin->w_cursor.lnum == curbuf->b_u_line_lnum)
+	curbuf->b_u_line_colnr = curwin->w_cursor.col;
+    curwin->w_cursor.col = t;
+    curwin->w_cursor.lnum = curbuf->b_u_line_lnum;
+}
+
+/*
+ * storage allocation for the undo lines and blocks of the current file
+ */
+
+/*
+ * Memory is allocated in relatively large blocks. These blocks are linked
+ * in the allocated block list, headed by curbuf->b_block_head. They are all
+ * freed when abandoning a file, so we don't have to free every single line.
+ * The list is kept sorted on memory address.
+ * block_alloc() allocates a block.
+ * m_blockfree() frees all blocks.
+ *
+ * The available chunks of memory are kept in free chunk lists. There is
+ * one free list for each block of allocated memory. The list is kept sorted
+ * on memory address.
+ * u_alloc_line() gets a chunk from the free lists.
+ * u_free_line() returns a chunk to the free lists.
+ * curbuf->b_m_search points to the chunk before the chunk that was
+ * freed/allocated the last time.
+ * curbuf->b_mb_current points to the b_head where curbuf->b_m_search
+ * points into the free list.
+ *
+ *
+ *  b_block_head     /---> block #1	/---> block #2
+ *	 mb_next ---/	    mb_next ---/       mb_next ---> NULL
+ *	 mb_info	    mb_info	       mb_info
+ *	    |		       |		  |
+ *	    V		       V		  V
+ *	  NULL		free chunk #1.1      free chunk #2.1
+ *			       |		  |
+ *			       V		  V
+ *			free chunk #1.2		 NULL
+ *			       |
+ *			       V
+ *			      NULL
+ *
+ * When a single free chunk list would have been used, it could take a lot
+ * of time in u_free_line() to find the correct place to insert a chunk in the
+ * free list. The single free list would become very long when many lines are
+ * changed (e.g. with :%s/^M$//).
+ */
+
+ /*
+  * this blocksize is used when allocating new lines
+  */
+#define MEMBLOCKSIZE 2044
+
+/*
+ * The size field contains the size of the chunk, including the size field
+ * itself.
+ *
+ * When the chunk is not in-use it is preceded with the m_info structure.
+ * The m_next field links it in one of the free chunk lists.
+ *
+ * On most unix systems structures have to be longword (32 or 64 bit) aligned.
+ * On most other systems they are short (16 bit) aligned.
+ */
+
+/* the structure definitions are now in structs.h */
+
+#ifdef ALIGN_LONG
+    /* size of m_size */
+# define M_OFFSET (sizeof(long_u))
+#else
+    /* size of m_size */
+# define M_OFFSET (sizeof(short_u))
+#endif
+
+/*
+ * Allocate a block of memory and link it in the allocated block list.
+ */
+    static char_u *
+u_blockalloc(size)
+    long_u	size;
+{
+    mblock_T	*p;
+    mblock_T	*mp, *next;
+
+    p = (mblock_T *)lalloc(size + sizeof(mblock_T), FALSE);
+    if (p != NULL)
+    {
+	 /* Insert the block into the allocated block list, keeping it
+		    sorted on address. */
+	for (mp = &curbuf->b_block_head;
+		(next = mp->mb_next) != NULL && next < p;
+			mp = next)
+	    ;
+	p->mb_next = next;		/* link in block list */
+	p->mb_size = size;
+	mp->mb_next = p;
+	p->mb_info.m_next = NULL;	/* clear free list */
+	p->mb_info.m_size = 0;
+	curbuf->b_mb_current = p;	/* remember current block */
+	curbuf->b_m_search = NULL;
+	p++;				/* return usable memory */
+    }
+    return (char_u *)p;
+}
+
+/*
+ * free all allocated memory blocks for the buffer 'buf'
+ */
+    void
+u_blockfree(buf)
+    buf_T	*buf;
+{
+    mblock_T	*p, *np;
+
+    for (p = buf->b_block_head.mb_next; p != NULL; p = np)
+    {
+	np = p->mb_next;
+	vim_free(p);
+    }
+    buf->b_block_head.mb_next = NULL;
+    buf->b_m_search = NULL;
+    buf->b_mb_current = NULL;
+}
+
+/*
+ * Free a chunk of memory for the current buffer.
+ * Insert the chunk into the correct free list, keeping it sorted on address.
+ */
+    static void
+u_free_line(ptr, keep)
+    char_u	*ptr;
+    int		keep;	/* don't free the block when it's empty */
+{
+    minfo_T	*next;
+    minfo_T	*prev, *curr;
+    minfo_T	*mp;
+    mblock_T	*nextb;
+    mblock_T	*prevb;
+
+    if (ptr == NULL || ptr == IObuff)
+	return;	/* illegal address can happen in out-of-memory situations */
+
+    mp = (minfo_T *)(ptr - M_OFFSET);
+
+    /* find block where chunk could be a part off */
+    /* if we change curbuf->b_mb_current, curbuf->b_m_search is set to NULL */
+    if (curbuf->b_mb_current == NULL || mp < (minfo_T *)curbuf->b_mb_current)
+    {
+	curbuf->b_mb_current = curbuf->b_block_head.mb_next;
+	curbuf->b_m_search = NULL;
+    }
+    if ((nextb = curbuf->b_mb_current->mb_next) != NULL
+						     && (minfo_T *)nextb < mp)
+    {
+	curbuf->b_mb_current = nextb;
+	curbuf->b_m_search = NULL;
+    }
+    while ((nextb = curbuf->b_mb_current->mb_next) != NULL
+						     && (minfo_T *)nextb < mp)
+	curbuf->b_mb_current = nextb;
+
+    curr = NULL;
+    /*
+     * If mp is smaller than curbuf->b_m_search->m_next go to the start of
+     * the free list
+     */
+    if (curbuf->b_m_search == NULL || mp < (curbuf->b_m_search->m_next))
+	next = &(curbuf->b_mb_current->mb_info);
+    else
+	next = curbuf->b_m_search;
+    /*
+     * The following loop is executed very often.
+     * Therefore it has been optimized at the cost of readability.
+     * Keep it fast!
+     */
+#ifdef SLOW_BUT_EASY_TO_READ
+    do
+    {
+	prev = curr;
+	curr = next;
+	next = next->m_next;
+    }
+    while (mp > next && next != NULL);
+#else
+    do					    /* first, middle, last */
+    {
+	prev = next->m_next;		    /* curr, next, prev */
+	if (prev == NULL || mp <= prev)
+	{
+	    prev = curr;
+	    curr = next;
+	    next = next->m_next;
+	    break;
+	}
+	curr = prev->m_next;		    /* next, prev, curr */
+	if (curr == NULL || mp <= curr)
+	{
+	    prev = next;
+	    curr = prev->m_next;
+	    next = curr->m_next;
+	    break;
+	}
+	next = curr->m_next;		    /* prev, curr, next */
+    }
+    while (mp > next && next != NULL);
+#endif
+
+    /* if *mp and *next are concatenated, join them into one chunk */
+    if ((char_u *)mp + mp->m_size == (char_u *)next)
+    {
+	mp->m_size += next->m_size;
+	mp->m_next = next->m_next;
+    }
+    else
+	mp->m_next = next;
+
+    /* if *curr and *mp are concatenated, join them */
+    if (prev != NULL && (char_u *)curr + curr->m_size == (char_u *)mp)
+    {
+	curr->m_size += mp->m_size;
+	curr->m_next = mp->m_next;
+	curbuf->b_m_search = prev;
+    }
+    else
+    {
+	curr->m_next = mp;
+	curbuf->b_m_search = curr;  /* put curbuf->b_m_search before freed
+				       chunk */
+    }
+
+    /*
+     * If the block only containes free memory now, release it.
+     */
+    if (!keep && curbuf->b_mb_current->mb_size
+			      == curbuf->b_mb_current->mb_info.m_next->m_size)
+    {
+	/* Find the block before the current one to be able to unlink it from
+	 * the list of blocks. */
+	prevb = &curbuf->b_block_head;
+	for (nextb = prevb->mb_next; nextb != curbuf->b_mb_current;
+						       nextb = nextb->mb_next)
+	    prevb = nextb;
+	prevb->mb_next = nextb->mb_next;
+	vim_free(nextb);
+	curbuf->b_mb_current = NULL;
+	curbuf->b_m_search = NULL;
+    }
+}
+
+/*
+ * Allocate and initialize a new line structure with room for at least
+ * 'size' characters plus a terminating NUL.
+ */
+    static char_u *
+u_alloc_line(size)
+    unsigned	size;
+{
+    minfo_T	*mp, *mprev, *mp2;
+    mblock_T	*mbp;
+    int		size_align;
+
+    /*
+     * Add room for size field and trailing NUL byte.
+     * Adjust for minimal size (must be able to store minfo_T
+     * plus a trailing NUL, so the chunk can be released again)
+     */
+    size += M_OFFSET + 1;
+    if (size < sizeof(minfo_T) + 1)
+	size = sizeof(minfo_T) + 1;
+
+    /*
+     * round size up for alignment
+     */
+    size_align = (size + ALIGN_MASK) & ~ALIGN_MASK;
+
+    /*
+     * If curbuf->b_m_search is NULL (uninitialized free list) start at
+     * curbuf->b_block_head
+     */
+    if (curbuf->b_mb_current == NULL || curbuf->b_m_search == NULL)
+    {
+	curbuf->b_mb_current = &curbuf->b_block_head;
+	curbuf->b_m_search = &(curbuf->b_block_head.mb_info);
+    }
+
+    /* search for space in free list */
+    mprev = curbuf->b_m_search;
+    mbp = curbuf->b_mb_current;
+    mp = curbuf->b_m_search->m_next;
+    if (mp == NULL)
+    {
+	if (mbp->mb_next)
+	    mbp = mbp->mb_next;
+	else
+	    mbp = &curbuf->b_block_head;
+	mp = curbuf->b_m_search = &(mbp->mb_info);
+    }
+    while (mp->m_size < size)
+    {
+	if (mp == curbuf->b_m_search)	    /* back where we started in free
+					       chunk list */
+	{
+	    if (mbp->mb_next)
+		mbp = mbp->mb_next;
+	    else
+		mbp = &curbuf->b_block_head;
+	    mp = curbuf->b_m_search = &(mbp->mb_info);
+	    if (mbp == curbuf->b_mb_current)	/* back where we started in
+						   block list */
+	    {
+		int	n = (size_align > (MEMBLOCKSIZE / 4)
+						 ? size_align : MEMBLOCKSIZE);
+
+		mp = (minfo_T *)u_blockalloc((long_u)n);
+		if (mp == NULL)
+		    return (NULL);
+		mp->m_size = n;
+		u_free_line((char_u *)mp + M_OFFSET, TRUE);
+		mp = curbuf->b_m_search;
+		mbp = curbuf->b_mb_current;
+	    }
+	}
+	mprev = mp;
+	if ((mp = mp->m_next) == NULL)	    /* at end of the list */
+	    mp = &(mbp->mb_info);	    /* wrap around to begin */
+    }
+
+    /* if the chunk we found is large enough, split it up in two */
+    if ((long)mp->m_size - size_align >= (long)(sizeof(minfo_T) + 1))
+    {
+	mp2 = (minfo_T *)((char_u *)mp + size_align);
+	mp2->m_size = mp->m_size - size_align;
+	mp2->m_next = mp->m_next;
+	mprev->m_next = mp2;
+	mp->m_size = size_align;
+    }
+    else		    /* remove *mp from the free list */
+    {
+	mprev->m_next = mp->m_next;
+    }
+    curbuf->b_m_search = mprev;
+    curbuf->b_mb_current = mbp;
+
+    mp = (minfo_T *)((char_u *)mp + M_OFFSET);
+    *(char_u *)mp = NUL;		    /* set the first byte to NUL */
+
+    return ((char_u *)mp);
+}
+
+/*
+ * u_save_line(): allocate memory with u_alloc_line() and copy line 'lnum'
+ * into it.
+ */
+    static char_u *
+u_save_line(lnum)
+    linenr_T	lnum;
+{
+    char_u	*src;
+    char_u	*dst;
+    unsigned	len;
+
+    src = ml_get(lnum);
+    len = (unsigned)STRLEN(src);
+    if ((dst = u_alloc_line(len)) != NULL)
+	mch_memmove(dst, src, (size_t)(len + 1));
+    return (dst);
+}
+
+/*
+ * Check if the 'modified' flag is set, or 'ff' has changed (only need to
+ * check the first character, because it can only be "dos", "unix" or "mac").
+ * "nofile" and "scratch" type buffers are considered to always be unchanged.
+ */
+    int
+bufIsChanged(buf)
+    buf_T	*buf;
+{
+    return
+#ifdef FEAT_QUICKFIX
+	    !bt_dontwrite(buf) &&
+#endif
+	    (buf->b_changed || file_ff_differs(buf));
+}
+
+    int
+curbufIsChanged()
+{
+    return
+#ifdef FEAT_QUICKFIX
+	!bt_dontwrite(curbuf) &&
+#endif
+	(curbuf->b_changed || file_ff_differs(curbuf));
+}