diff --git a/src/regexp.c b/src/regexp.c
index e456b5d..a1f71ab 100644
--- a/src/regexp.c
+++ b/src/regexp.c
@@ -38,9 +38,20 @@
  * Named character class support added by Walter Briscoe (1998 Jul 01)
  */
 
+/* Uncomment the first if you do not want to see debugging logs or files
+ * related to regular expressions, even when compiling with -DDEBUG.
+ * Uncomment the second to get the regexp debugging. */
+/* #undef DEBUG */
+/* #define DEBUG */
+
 #include "vim.h"
 
-#undef DEBUG
+#ifdef DEBUG
+/* show/save debugging data when BT engine is used */
+# define BT_REGEXP_DUMP
+/* save the debugging data to a file instead of displaying it */
+# define BT_REGEXP_LOG
+#endif
 
 /*
  * The "internal use only" fields in regexp.h are present to pass info from
@@ -326,9 +337,10 @@
 /* Used for an error (down from) vim_regcomp(): give the error message, set
  * rc_did_emsg and return NULL */
 #define EMSG_RET_NULL(m) return (EMSG(m), rc_did_emsg = TRUE, (void *)NULL)
-#define EMSG_M_RET_NULL(m, c) return (EMSG2((m), (c) ? "" : "\\"), rc_did_emsg = TRUE, (void *)NULL)
 #define EMSG_RET_FAIL(m) return (EMSG(m), rc_did_emsg = TRUE, FAIL)
-#define EMSG_ONE_RET_NULL EMSG_M_RET_NULL(_("E369: invalid item in %s%%[]"), reg_magic == MAGIC_ALL)
+#define EMSG2_RET_NULL(m, c) return (EMSG2((m), (c) ? "" : "\\"), rc_did_emsg = TRUE, (void *)NULL)
+#define EMSG2_RET_FAIL(m, c) return (EMSG2((m), (c) ? "" : "\\"), rc_did_emsg = TRUE, FAIL)
+#define EMSG_ONE_RET_NULL EMSG2_RET_NULL(_("E369: invalid item in %s%%[]"), reg_magic == MAGIC_ALL)
 
 #define MAX_LIMIT	(32767L << 16L)
 
@@ -336,11 +348,18 @@
 static int cstrncmp __ARGS((char_u *s1, char_u *s2, int *n));
 static char_u *cstrchr __ARGS((char_u *, int));
 
+#ifdef BT_REGEXP_DUMP
+static void	regdump __ARGS((char_u *, bt_regprog_T *));
+#endif
 #ifdef DEBUG
-static void	regdump __ARGS((char_u *, regprog_T *));
 static char_u	*regprop __ARGS((char_u *));
 #endif
 
+static char_u e_missingbracket[] = N_("E769: Missing ] after %s[");
+static char_u e_unmatchedpp[] = N_("E53: Unmatched %s%%(");
+static char_u e_unmatchedp[] = N_("E54: Unmatched %s(");
+static char_u e_unmatchedpar[] = N_("E55: Unmatched %s)");
+
 #define NOT_MULTI	0
 #define MULTI_ONE	1
 #define MULTI_MULT	2
@@ -630,7 +649,13 @@
 };
 #endif
 
-static int	curchr;
+static int	curchr;		/* currently parsed character */
+/* Previous character.  Note: prevchr is sometimes -1 when we are not at the
+ * start, eg in /[ ^I]^ the pattern was never found even if it existed,
+ * because ^ was taken to be magic -- webb */
+static int	prevchr;
+static int	prevprevchr;	/* previous-previous character */
+static int	nextchr;	/* used for ungetchr() */
 
 /* arguments for reg() */
 #define REG_NOPAREN	0	/* toplevel reg() */
@@ -680,6 +705,9 @@
 static void	regtail __ARGS((char_u *, char_u *));
 static void	regoptail __ARGS((char_u *, char_u *));
 
+static regengine_T bt_regengine;
+static regengine_T nfa_regengine;
+
 /*
  * Return TRUE if compiled regular expression "prog" can match a line break.
  */
@@ -762,6 +790,7 @@
 /*
  * Produce the bytes for equivalence class "c".
  * Currently only handles latin1, latin9 and utf-8.
+ * NOTE: When changing this function, also change nfa_emit_equi_class()
  */
     static void
 reg_equi_class(c)
@@ -1239,8 +1268,11 @@
     return p;
 }
 
+static regprog_T    *bt_regcomp __ARGS((char_u *expr, int re_flags));
+
 /*
- * vim_regcomp() - compile a regular expression into internal code
+ * bt_regcomp() - compile a regular expression into internal code for the
+ * traditional back track matcher.
  * Returns the program in allocated space.  Returns NULL for an error.
  *
  * We can't allocate space until we know how big the compiled form will be,
@@ -1259,12 +1291,12 @@
  * of the structure of the compiled regexp.
  * "re_flags": RE_MAGIC and/or RE_STRING.
  */
-    regprog_T *
-vim_regcomp(expr, re_flags)
+    static regprog_T *
+bt_regcomp(expr, re_flags)
     char_u	*expr;
     int		re_flags;
 {
-    regprog_T	*r;
+    bt_regprog_T    *r;
     char_u	*scan;
     char_u	*longest;
     int		len;
@@ -1291,7 +1323,7 @@
 #endif
 
     /* Allocate space. */
-    r = (regprog_T *)lalloc(sizeof(regprog_T) + regsize, TRUE);
+    r = (bt_regprog_T *)lalloc(sizeof(bt_regprog_T) + regsize, TRUE);
     if (r == NULL)
 	return NULL;
 
@@ -1386,10 +1418,11 @@
 	    r->regmlen = len;
 	}
     }
-#ifdef DEBUG
+#ifdef BT_REGEXP_DUMP
     regdump(expr, r);
 #endif
-    return r;
+    r->engine = &bt_regengine;
+    return (regprog_T *)r;
 }
 
 /*
@@ -1436,7 +1469,7 @@
 #endif
 
 /*
- * reg - regular expression, i.e. main body or parenthesized thing
+ * Parse regular expression, i.e. main body or parenthesized thing.
  *
  * Caller must absorb opening parenthesis.
  *
@@ -1473,7 +1506,7 @@
     {
 	/* Make a MOPEN node. */
 	if (regnpar >= NSUBEXP)
-	    EMSG_M_RET_NULL(_("E51: Too many %s("), reg_magic == MAGIC_ALL);
+	    EMSG2_RET_NULL(_("E51: Too many %s("), reg_magic == MAGIC_ALL);
 	parno = regnpar;
 	++regnpar;
 	ret = regnode(MOPEN + parno);
@@ -1534,14 +1567,14 @@
 	else
 #endif
 	    if (paren == REG_NPAREN)
-	    EMSG_M_RET_NULL(_("E53: Unmatched %s%%("), reg_magic == MAGIC_ALL);
+	    EMSG2_RET_NULL(_(e_unmatchedpp), reg_magic == MAGIC_ALL);
 	else
-	    EMSG_M_RET_NULL(_("E54: Unmatched %s("), reg_magic == MAGIC_ALL);
+	    EMSG2_RET_NULL(_(e_unmatchedp), reg_magic == MAGIC_ALL);
     }
     else if (paren == REG_NOPAREN && peekchr() != NUL)
     {
 	if (curchr == Magic(')'))
-	    EMSG_M_RET_NULL(_("E55: Unmatched %s)"), reg_magic == MAGIC_ALL);
+	    EMSG2_RET_NULL(_(e_unmatchedpar), reg_magic == MAGIC_ALL);
 	else
 	    EMSG_RET_NULL(_(e_trailing));	/* "Can't happen". */
 	/* NOTREACHED */
@@ -1556,7 +1589,7 @@
 }
 
 /*
- * Handle one alternative of an | operator.
+ * Parse one alternative of an | operator.
  * Implements the & operator.
  */
     static char_u *
@@ -1599,7 +1632,7 @@
 }
 
 /*
- * Handle one alternative of an | or & operator.
+ * Parse one alternative of an | or & operator.
  * Implements the concatenation operator.
  */
     static char_u *
@@ -1679,7 +1712,7 @@
 }
 
 /*
- * regpiece - something followed by possible [*+=]
+ * Parse something followed by possible [*+=].
  *
  * Note that the branching code sequences used for = and the general cases
  * of * and + are somewhat optimized:  they use the same NOTHING node as
@@ -1759,7 +1792,7 @@
 			      }
 		}
 		if (lop == END)
-		    EMSG_M_RET_NULL(_("E59: invalid character after %s@"),
+		    EMSG2_RET_NULL(_("E59: invalid character after %s@"),
 						      reg_magic == MAGIC_ALL);
 		/* Look behind must match with behind_pos. */
 		if (lop == BEHIND || lop == NOBEHIND)
@@ -1793,7 +1826,7 @@
 	    else
 	    {
 		if (num_complex_braces >= 10)
-		    EMSG_M_RET_NULL(_("E60: Too many complex %s{...}s"),
+		    EMSG2_RET_NULL(_("E60: Too many complex %s{...}s"),
 						      reg_magic == MAGIC_ALL);
 		reginsert(BRACE_COMPLEX + num_complex_braces, ret);
 		regoptail(ret, regnode(BACK));
@@ -1820,8 +1853,20 @@
     return ret;
 }
 
+/* When making changes to classchars also change nfa_classcodes. */
+static char_u	*classchars = (char_u *)".iIkKfFpPsSdDxXoOwWhHaAlLuU";
+static int	classcodes[] = {
+    ANY, IDENT, SIDENT, KWORD, SKWORD,
+    FNAME, SFNAME, PRINT, SPRINT,
+    WHITE, NWHITE, DIGIT, NDIGIT,
+    HEX, NHEX, OCTAL, NOCTAL,
+    WORD, NWORD, HEAD, NHEAD,
+    ALPHA, NALPHA, LOWER, NLOWER,
+    UPPER, NUPPER
+};
+
 /*
- * regatom - the lowest level
+ * Parse the lowest level.
  *
  * Optimization:  gobbles an entire sequence of ordinary characters so that
  * it can turn them into a single node, which is smaller to store and
@@ -1836,15 +1881,6 @@
     int		    cpo_lit;	    /* 'cpoptions' contains 'l' flag */
     int		    cpo_bsl;	    /* 'cpoptions' contains '\' flag */
     int		    c;
-    static char_u   *classchars = (char_u *)".iIkKfFpPsSdDxXoOwWhHaAlLuU";
-    static int	    classcodes[] = {ANY, IDENT, SIDENT, KWORD, SKWORD,
-				    FNAME, SFNAME, PRINT, SPRINT,
-				    WHITE, NWHITE, DIGIT, NDIGIT,
-				    HEX, NHEX, OCTAL, NOCTAL,
-				    WORD, NWORD, HEAD, NHEAD,
-				    ALPHA, NALPHA, LOWER, NLOWER,
-				    UPPER, NUPPER
-				    };
     char_u	    *p;
     int		    extra = 0;
 
@@ -2140,7 +2176,7 @@
 			      while ((c = getchr()) != ']')
 			      {
 				  if (c == NUL)
-				      EMSG_M_RET_NULL(_("E69: Missing ] after %s%%["),
+				      EMSG2_RET_NULL(_("E69: Missing ] after %s%%["),
 						      reg_magic == MAGIC_ALL);
 				  br = regnode(BRANCH);
 				  if (ret == NULL)
@@ -2156,7 +2192,7 @@
 				      return NULL;
 			      }
 			      if (ret == NULL)
-				  EMSG_M_RET_NULL(_("E70: Empty %s%%[]"),
+				  EMSG2_RET_NULL(_("E70: Empty %s%%[]"),
 						      reg_magic == MAGIC_ALL);
 			      lastbranch = regnode(BRANCH);
 			      br = regnode(NOTHING);
@@ -2200,7 +2236,7 @@
 			      }
 
 			      if (i < 0)
-				  EMSG_M_RET_NULL(
+				  EMSG2_RET_NULL(
 					_("E678: Invalid character after %s%%[dxouU]"),
 					reg_magic == MAGIC_ALL);
 #ifdef FEAT_MBYTE
@@ -2272,7 +2308,7 @@
 			      }
 			  }
 
-			  EMSG_M_RET_NULL(_("E71: Invalid character after %s%%"),
+			  EMSG2_RET_NULL(_("E71: Invalid character after %s%%"),
 						      reg_magic == MAGIC_ALL);
 	    }
 	}
@@ -2567,8 +2603,7 @@
 		break;
 	    }
 	    else if (reg_strict)
-		EMSG_M_RET_NULL(_("E769: Missing ] after %s["),
-						       reg_magic > MAGIC_OFF);
+		EMSG2_RET_NULL(_(e_missingbracket), reg_magic > MAGIC_OFF);
 	}
 	/* FALLTHROUGH */
 
@@ -2659,7 +2694,7 @@
 #endif
 
 /*
- * emit a node
+ * Emit a node.
  * Return pointer to generated code.
  */
     static char_u *
@@ -2711,7 +2746,7 @@
 #endif
 
 /*
- * reginsert - insert an operator in front of already-emitted operand
+ * Insert an operator in front of already-emitted operand
  *
  * Means relocating the operand.
  */
@@ -2742,7 +2777,7 @@
 }
 
 /*
- * reginsert_limits - insert an operator in front of already-emitted operand.
+ * Insert an operator in front of already-emitted operand.
  * The operator has the given limit values as operands.  Also set next pointer.
  *
  * Means relocating the operand.
@@ -2794,7 +2829,7 @@
 }
 
 /*
- * regtail - set the next-pointer at the end of a node chain
+ * Set the next-pointer at the end of a node chain.
  */
     static void
 regtail(p, val)
@@ -2835,7 +2870,7 @@
 }
 
 /*
- * regoptail - regtail on item after a BRANCH; nop if none
+ * Like regtail, on item after a BRANCH; nop if none.
  */
     static void
 regoptail(p, val)
@@ -2851,22 +2886,15 @@
 }
 
 /*
- * getchr() - get the next character from the pattern. We know about
- * magic and such, so therefore we need a lexical analyzer.
+ * Functions for getting characters from the regexp input.
  */
 
-/* static int	    curchr; */
-static int	prevprevchr;
-static int	prevchr;
-static int	nextchr;    /* used for ungetchr() */
-/*
- * Note: prevchr is sometimes -1 when we are not at the start,
- * eg in /[ ^I]^ the pattern was never found even if it existed, because ^ was
- * taken to be magic -- webb
- */
 static int	at_start;	/* True when on the first character */
 static int	prev_at_start;  /* True when on the second character */
 
+/*
+ * Start parsing at "str".
+ */
     static void
 initchr(str)
     char_u *str;
@@ -2878,6 +2906,9 @@
     prev_at_start = FALSE;
 }
 
+/*
+ * Get the next character without advancing.
+ */
     static int
 peekchr()
 {
@@ -3086,6 +3117,10 @@
     prevprevchr = prpr;
 }
 
+/*
+ * Get the next character from the pattern. We know about magic and such, so
+ * therefore we need a lexical analyzer.
+ */
     static int
 getchr()
 {
@@ -3340,8 +3375,8 @@
 } regbehind_T;
 
 static char_u	*reg_getline __ARGS((linenr_T lnum));
-static long	vim_regexec_both __ARGS((char_u *line, colnr_T col, proftime_T *tm));
-static long	regtry __ARGS((regprog_T *prog, colnr_T col));
+static long	bt_regexec_both __ARGS((char_u *line, colnr_T col, proftime_T *tm));
+static long	regtry __ARGS((bt_regprog_T *prog, colnr_T col));
 static void	cleanup_subexpr __ARGS((void));
 #ifdef FEAT_SYN_HL
 static void	cleanup_zsubexpr __ARGS((void));
@@ -3398,7 +3433,7 @@
 /*
  * Sometimes need to save a copy of a line.  Since alloc()/free() is very
  * slow, we keep one allocated piece of memory and only re-allocate it when
- * it's too small.  It's freed in vim_regexec_both() when finished.
+ * it's too small.  It's freed in bt_regexec_both() when finished.
  */
 static char_u	*reg_tofree = NULL;
 static unsigned	reg_tofreelen;
@@ -3556,6 +3591,8 @@
 /* TRUE if using multi-line regexp. */
 #define REG_MULTI	(reg_match == NULL)
 
+static int  bt_regexec __ARGS((regmatch_T *rmp, char_u *line, colnr_T col));
+
 /*
  * Match a regexp against a string.
  * "rmp->regprog" is a compiled regexp as returned by vim_regcomp().
@@ -3563,8 +3600,8 @@
  *
  * Return TRUE if there is a match, FALSE if not.
  */
-    int
-vim_regexec(rmp, line, col)
+    static int
+bt_regexec(rmp, line, col)
     regmatch_T	*rmp;
     char_u	*line;	/* string to match against */
     colnr_T	col;	/* column to start looking for match */
@@ -3580,16 +3617,19 @@
     ireg_icombine = FALSE;
 #endif
     ireg_maxcol = 0;
-    return (vim_regexec_both(line, col, NULL) != 0);
+    return (bt_regexec_both(line, col, NULL) != 0);
 }
 
 #if defined(FEAT_MODIFY_FNAME) || defined(FEAT_EVAL) \
 	|| defined(FIND_REPLACE_DIALOG) || defined(PROTO)
+
+static int  bt_regexec_nl __ARGS((regmatch_T *rmp, char_u *line, colnr_T col));
+
 /*
  * Like vim_regexec(), but consider a "\n" in "line" to be a line break.
  */
-    int
-vim_regexec_nl(rmp, line, col)
+    static int
+bt_regexec_nl(rmp, line, col)
     regmatch_T	*rmp;
     char_u	*line;	/* string to match against */
     colnr_T	col;	/* column to start looking for match */
@@ -3605,10 +3645,12 @@
     ireg_icombine = FALSE;
 #endif
     ireg_maxcol = 0;
-    return (vim_regexec_both(line, col, NULL) != 0);
+    return (bt_regexec_both(line, col, NULL) != 0);
 }
 #endif
 
+static long bt_regexec_multi __ARGS((regmmatch_T *rmp, win_T *win, buf_T *buf, linenr_T lnum, colnr_T col, proftime_T *tm));
+
 /*
  * Match a regexp against multiple lines.
  * "rmp->regprog" is a compiled regexp as returned by vim_regcomp().
@@ -3617,8 +3659,8 @@
  * Return zero if there is no match.  Return number of lines contained in the
  * match otherwise.
  */
-    long
-vim_regexec_multi(rmp, win, buf, lnum, col, tm)
+    static long
+bt_regexec_multi(rmp, win, buf, lnum, col, tm)
     regmmatch_T	*rmp;
     win_T	*win;		/* window in which to search or NULL */
     buf_T	*buf;		/* buffer in which to search */
@@ -3641,7 +3683,7 @@
 #endif
     ireg_maxcol = rmp->rmm_maxcol;
 
-    r = vim_regexec_both(NULL, col, tm);
+    r = bt_regexec_both(NULL, col, tm);
 
     return r;
 }
@@ -3651,12 +3693,12 @@
  * lines ("line" is NULL, use reg_getline()).
  */
     static long
-vim_regexec_both(line, col, tm)
+bt_regexec_both(line, col, tm)
     char_u	*line;
     colnr_T	col;		/* column to start looking for match */
     proftime_T	*tm UNUSED;	/* timeout limit or NULL */
 {
-    regprog_T	*prog;
+    bt_regprog_T	*prog;
     char_u	*s;
     long	retval = 0L;
 
@@ -3682,14 +3724,14 @@
 
     if (REG_MULTI)
     {
-	prog = reg_mmatch->regprog;
+	prog = (bt_regprog_T *)reg_mmatch->regprog;
 	line = reg_getline((linenr_T)0);
 	reg_startpos = reg_mmatch->startpos;
 	reg_endpos = reg_mmatch->endpos;
     }
     else
     {
-	prog = reg_match->regprog;
+	prog = (bt_regprog_T *)reg_match->regprog;
 	reg_startp = reg_match->startp;
 	reg_endp = reg_match->endp;
     }
@@ -3931,7 +3973,7 @@
  */
     static long
 regtry(prog, col)
-    regprog_T	*prog;
+    bt_regprog_T    *prog;
     colnr_T	col;
 {
     reginput = regline + col;
@@ -4063,7 +4105,7 @@
 #define RA_NOMATCH	5	/* didn't match */
 
   /* Make "regstack" and "backpos" empty.  They are allocated and freed in
-   * vim_regexec_both() to reduce malloc()/free() calls. */
+   * bt_regexec_both() to reduce malloc()/free() calls. */
   regstack.ga_len = 0;
   backpos.ga_len = 0;
 
@@ -4072,14 +4114,14 @@
    */
   for (;;)
   {
-    /* Some patterns my cause a long time to match, even though they are not
+    /* Some patterns may cause a long time to match, even though they are not
      * illegal.  E.g., "\([a-z]\+\)\+Q".  Allow breaking them with CTRL-C. */
     fast_breakcheck();
 
 #ifdef DEBUG
     if (scan != NULL && regnarrate)
     {
-	mch_errmsg(regprop(scan));
+	mch_errmsg((char *)regprop(scan));
 	mch_errmsg("(\n");
     }
 #endif
@@ -4100,7 +4142,7 @@
 #ifdef DEBUG
 	if (regnarrate)
 	{
-	    mch_errmsg(regprop(scan));
+	    mch_errmsg((char *)regprop(scan));
 	    mch_errmsg("...\n");
 # ifdef FEAT_SYN_HL
 	    if (re_extmatch_in != NULL)
@@ -4112,7 +4154,7 @@
 		{
 		    mch_errmsg("    \"");
 		    if (re_extmatch_in->matches[i] != NULL)
-			mch_errmsg(re_extmatch_in->matches[i]);
+			mch_errmsg((char *)re_extmatch_in->matches[i]);
 		    mch_errmsg("\"\n");
 		}
 	    }
@@ -6091,9 +6133,14 @@
     static int
 prog_magic_wrong()
 {
-    if (UCHARAT(REG_MULTI
-		? reg_mmatch->regprog->program
-		: reg_match->regprog->program) != REGMAGIC)
+    regprog_T	*prog;
+
+    prog = REG_MULTI ? reg_mmatch->regprog : reg_match->regprog;
+    if (prog->engine == &nfa_regengine)
+	/* For NFA matcher we don't check the magic */
+	return FALSE;
+
+    if (UCHARAT(((bt_regprog_T *)prog)->program) != REGMAGIC)
     {
 	EMSG(_(e_re_corr));
 	return TRUE;
@@ -6318,7 +6365,7 @@
 }
 
 
-#ifdef DEBUG
+#ifdef BT_REGEXP_DUMP
 
 /*
  * regdump - dump a regexp onto stdout in vaguely comprehensible form
@@ -6326,14 +6373,22 @@
     static void
 regdump(pattern, r)
     char_u	*pattern;
-    regprog_T	*r;
+    bt_regprog_T	*r;
 {
     char_u  *s;
     int	    op = EXACTLY;	/* Arbitrary non-END op. */
     char_u  *next;
     char_u  *end = NULL;
+    FILE    *f;
 
-    printf("\r\nregcomp(%s):\r\n", pattern);
+#ifdef BT_REGEXP_LOG
+    f = fopen("bt_regexp_log.log", "a");
+#else
+    f = stdout;
+#endif
+    if (f == NULL)
+	return;
+    fprintf(f, "-------------------------------------\n\r\nregcomp(%s):\r\n", pattern);
 
     s = r->program + 1;
     /*
@@ -6343,18 +6398,18 @@
     while (op != END || s <= end)
     {
 	op = OP(s);
-	printf("%2d%s", (int)(s - r->program), regprop(s)); /* Where, what. */
+	fprintf(f, "%2d%s", (int)(s - r->program), regprop(s)); /* Where, what. */
 	next = regnext(s);
 	if (next == NULL)	/* Next ptr. */
-	    printf("(0)");
+	    fprintf(f, "(0)");
 	else
-	    printf("(%d)", (int)((s - r->program) + (next - s)));
+	    fprintf(f, "(%d)", (int)((s - r->program) + (next - s)));
 	if (end < next)
 	    end = next;
 	if (op == BRACE_LIMITS)
 	{
 	    /* Two short ints */
-	    printf(" minval %ld, maxval %ld", OPERAND_MIN(s), OPERAND_MAX(s));
+	    fprintf(f, " minval %ld, maxval %ld", OPERAND_MIN(s), OPERAND_MAX(s));
 	    s += 8;
 	}
 	s += 3;
@@ -6363,25 +6418,33 @@
 		|| op == EXACTLY)
 	{
 	    /* Literal string, where present. */
+	    fprintf(f, "\nxxxxxxxxx\n");
 	    while (*s != NUL)
-		printf("%c", *s++);
+		fprintf(f, "%c", *s++);
+	    fprintf(f, "\nxxxxxxxxx\n");
 	    s++;
 	}
-	printf("\r\n");
+	fprintf(f, "\r\n");
     }
 
     /* Header fields of interest. */
     if (r->regstart != NUL)
-	printf("start `%s' 0x%x; ", r->regstart < 256
+	fprintf(f, "start `%s' 0x%x; ", r->regstart < 256
 		? (char *)transchar(r->regstart)
 		: "multibyte", r->regstart);
     if (r->reganch)
-	printf("anchored; ");
+	fprintf(f, "anchored; ");
     if (r->regmust != NULL)
-	printf("must have \"%s\"", r->regmust);
-    printf("\r\n");
-}
+	fprintf(f, "must have \"%s\"", r->regmust);
+    fprintf(f, "\r\n");
 
+#ifdef BT_REGEXP_LOG
+    fclose(f);
+#endif
+}
+#endif	    /* BT_REGEXP_DUMP */
+
+#ifdef DEBUG
 /*
  * regprop - printable representation of opcode
  */
@@ -6389,12 +6452,12 @@
 regprop(op)
     char_u	   *op;
 {
-    char_u	    *p;
-    static char_u   buf[50];
+    char	    *p;
+    static char	    buf[50];
 
-    (void) strcpy(buf, ":");
+    STRCPY(buf, ":");
 
-    switch (OP(op))
+    switch ((int) OP(op))
     {
       case BOL:
 	p = "BOL";
@@ -6761,10 +6824,10 @@
 	break;
     }
     if (p != NULL)
-	(void) strcat(buf, p);
-    return buf;
+	STRCAT(buf, p);
+    return (char_u *)buf;
 }
-#endif
+#endif	    /* DEBUG */
 
 #ifdef FEAT_MBYTE
 static void mb_decompose __ARGS((int c, int *c1, int *c2, int *c3));
@@ -7667,3 +7730,187 @@
     return retval;
 }
 #endif
+
+static regengine_T bt_regengine =
+{
+    bt_regcomp,
+    bt_regexec,
+#if defined(FEAT_MODIFY_FNAME) || defined(FEAT_EVAL) \
+	|| defined(FIND_REPLACE_DIALOG) || defined(PROTO)
+    bt_regexec_nl,
+#endif
+    bt_regexec_multi
+#ifdef DEBUG
+    ,(char_u *)""
+#endif
+};
+
+
+#include "regexp_nfa.c"
+
+static regengine_T nfa_regengine =
+{
+    nfa_regcomp,
+    nfa_regexec,
+#if defined(FEAT_MODIFY_FNAME) || defined(FEAT_EVAL) \
+	|| defined(FIND_REPLACE_DIALOG) || defined(PROTO)
+    nfa_regexec_nl,
+#endif
+    nfa_regexec_multi
+#ifdef DEBUG
+    ,(char_u *)""
+#endif
+};
+
+/* Which regexp engine to use? Needed for vim_regcomp().
+ * Must match with 'regexpengine'. */
+static int regexp_engine = 0;
+#define	    AUTOMATIC_ENGINE	0
+#define	    BACKTRACKING_ENGINE	1
+#define	    NFA_ENGINE		2
+#ifdef DEBUG
+static char_u regname[][30] = {
+		    "AUTOMATIC Regexp Engine",
+		    "BACKTACKING Regexp Engine",
+		    "NFA Regexp Engine"
+			    };
+#endif
+
+/*
+ * Compile a regular expression into internal code.
+ * Returns the program in allocated memory.  Returns NULL for an error.
+ */
+    regprog_T *
+vim_regcomp(expr_arg, re_flags)
+    char_u	*expr_arg;
+    int		re_flags;
+{
+    regprog_T   *prog = NULL;
+    char_u	*expr = expr_arg;
+
+    syntax_error = FALSE;
+    regexp_engine = p_re;
+
+    /* Check for prefix "\%#=", that sets the regexp engine */
+    if (STRNCMP(expr, "\\%#=", 4) == 0)
+    {
+	int newengine = expr[4] - '0';
+
+	if (newengine == AUTOMATIC_ENGINE
+	    || newengine == BACKTRACKING_ENGINE
+	    || newengine == NFA_ENGINE)
+	{
+	    regexp_engine = expr[4] - '0';
+	    expr += 5;
+#ifdef DEBUG
+	    EMSG3("New regexp mode selected (%d): %s", regexp_engine,
+						    regname[newengine]);
+#endif
+	}
+	else
+	{
+	    EMSG(_("E864: \\%#= can only be followed by 0, 1, or 2. The automatic engine will be used "));
+	    regexp_engine = AUTOMATIC_ENGINE;
+	}
+    }
+#ifdef DEBUG
+    bt_regengine.expr = expr;
+    nfa_regengine.expr = expr;
+#endif
+
+    /*
+     * First try the NFA engine, unless backtracking was requested.
+     */
+    if (regexp_engine != BACKTRACKING_ENGINE)
+        prog = nfa_regengine.regcomp(expr, re_flags);
+    else
+	prog = bt_regengine.regcomp(expr, re_flags);
+
+    if (prog == NULL)	    /* error compiling regexp with initial engine */
+    {
+#ifdef DEBUG
+	if (regexp_engine != BACKTRACKING_ENGINE)   /* debugging log for NFA */
+	{
+	    FILE *f;
+	    f = fopen("debug.log", "a");
+	    if (f)
+	    {
+		if (!syntax_error)
+		    fprintf(f, "NFA engine could not handle \"%s\"\n", expr);
+		else
+		    fprintf(f, "Syntax error in \"%s\"\n", expr);
+		fclose(f);
+	    }
+	    else
+		EMSG("(NFA) Could not open \"debug.log\" to write !!!");
+	    /*
+	    if (syntax_error)
+		EMSG("NFA Regexp: Syntax Error !");
+	    */
+	}
+#endif
+	/*
+	 * If NFA engine failed, then revert to the backtracking engine.
+	 * Except when there was a syntax error, which was properly handled by
+	 * NFA engine.
+	 */
+	if (regexp_engine == AUTOMATIC_ENGINE)
+	    if (!syntax_error)
+		prog = bt_regengine.regcomp(expr, re_flags);
+
+    }	    /* endif prog==NULL */
+
+
+    return prog;
+}
+
+/*
+ * Match a regexp against a string.
+ * "rmp->regprog" is a compiled regexp as returned by vim_regcomp().
+ * Uses curbuf for line count and 'iskeyword'.
+ *
+ * Return TRUE if there is a match, FALSE if not.
+ */
+    int
+vim_regexec(rmp, line, col)
+    regmatch_T *rmp;
+    char_u      *line;  /* string to match against */
+    colnr_T     col;    /* column to start looking for match */
+{
+    return rmp->regprog->engine->regexec(rmp, line, col);
+}
+
+#if defined(FEAT_MODIFY_FNAME) || defined(FEAT_EVAL) \
+	|| defined(FIND_REPLACE_DIALOG) || defined(PROTO)
+/*
+ * Like vim_regexec(), but consider a "\n" in "line" to be a line break.
+ */
+    int
+vim_regexec_nl(rmp, line, col)
+    regmatch_T *rmp;
+    char_u *line;
+    colnr_T col;
+{
+    return rmp->regprog->engine->regexec_nl(rmp, line, col);
+}
+#endif
+
+/*
+ * Match a regexp against multiple lines.
+ * "rmp->regprog" is a compiled regexp as returned by vim_regcomp().
+ * Uses curbuf for line count and 'iskeyword'.
+ *
+ * Return zero if there is no match.  Return number of lines contained in the
+ * match otherwise.
+ */
+    long
+vim_regexec_multi(rmp, win, buf, lnum, col, tm)
+    regmmatch_T *rmp;
+    win_T       *win;           /* window in which to search or NULL */
+    buf_T       *buf;           /* buffer in which to search */
+    linenr_T    lnum;           /* nr of line to start looking for match */
+    colnr_T     col;            /* column to start looking for match */
+    proftime_T	*tm;		/* timeout limit or NULL */
+{
+    return rmp->regprog->engine->regexec_multi(rmp, win, buf, lnum, col, tm);
+}