new fnmatch implementation

unlike the old one, this one's algorithm does not suffer from
potential stack overflow issues or pathologically bad performance on
certain patterns. instead of backtracking, it uses a matching
algorithm which I have not seen before (unsure whether I invented or
re-invented it) that runs in O(1) space and O(nm) time. it may be
possible to improve the time to O(n), but not without significantly
greater complexity.

src/regex/fnmatch.c

@@ -1,157 +1,299 @@
-#include <fnmatch.h>
-#include <wctype.h>
+/*
+ * An implementation of what I call the "Sea of Stars" algorithm for
+ * POSIX fnmatch(). The basic idea is that we factor the pattern into
+ * a head component (which we match first and can reject without ever
+ * measuring the length of the string), an optional tail component
+ * (which only exists if the pattern contains at least one star), and
+ * an optional "sea of stars", a set of star-separated components
+ * between the head and tail. After the head and tail matches have
+ * been removed from the input string, the components in the "sea of
+ * stars" are matched sequentially by searching for their first
+ * occurrence past the end of the previous match.
+ *
+ * - Rich Felker, April 2012
+ */
+
 #include <string.h>
-#include <wchar.h>
+#include <fnmatch.h>
 #include <stdlib.h>
-#include <limits.h>
+#include <wchar.h>
+#include <wctype.h>
 
-static int next(const char **s)
+#define END -1
+#define UNMATCHABLE -2
+#define BRACKET -3
+#define QUESTION -4
+#define STAR -5
+
+static int str_next(const char *str, size_t n, size_t *step)
 {
-	wchar_t c;
-	int l = mbtowc(&c, *s, MB_LEN_MAX);
-	/* hack to allow literal matches of invalid byte sequences */
-	if (l < 0) return (unsigned char)*(*s)++ - 0x100;
-	*s += l;
-	return c;
+	if (!n) {
+		*step = 0;
+		return 0;
+	}
+	if (str[0] >= 128U) {
+		wchar_t wc;
+		int k = mbtowc(&wc, str, n);
+		if (k<0) {
+			*step = 1;
+			return -1;
+		}
+		*step = k;
+		return wc;
+	}
+	*step = 1;
+	return str[0];
 }
 
-#define BRACKET_ERROR  -0x100
-#define BRACKET_NOCHAR -0x101
-
-static int bracket_next(const char **s)
+static int pat_next(const char *pat, size_t m, size_t *step, int flags)
 {
-	int c;
-	int type;
-	if (**s == '[') {
-		type = *(*s+1);
-		if (type == '.' || type == '=') {
-			*s += 2;
-			c = next(s);
-			if (c <= 0) return BRACKET_ERROR;
-			if (**s == type && *(*s+1) == ']') {
-				*s += 2;
-				return c;
+	int esc = 0;
+	if (!m || !*pat) {
+		*step = 0;
+		return END;
+	}
+	*step = 1;
+	if (pat[0]=='\\' && !(flags & FNM_NOESCAPE)) {
+		*step = 2;
+		pat++;
+		esc = 1;
+		goto escaped;
+	}
+	if (pat[0]=='[') {
+		size_t k = 1;
+		if (k<m) if (pat[k] == '^' || pat[k] == '!') k++;
+		if (k<m) if (pat[k] == ']') k++;
+		for (; k<m && pat[k] && pat[k]!=']'; k++) {
+			if (k+1<m && pat[k+1] && pat[k]=='[' && (pat[k+1]==':' || pat[k+1]=='.' || pat[k+1]=='=')) {
+				int z = pat[k+1];
+				k+=2;
+				if (k<m && pat[k]) k++;
+				while (k<m && pat[k] && (pat[k-1]!=z || pat[k]!=']')) k++;
+				if (k==m || !pat[k]) break;
 			}
-			for (; **s && (**s != type || *(*s+1) != ']'); (*s)++);
-			if (!**s) return BRACKET_ERROR;
-			*s += 2;
-			return BRACKET_NOCHAR;
 		}
+		if (k==m || !pat[k]) {
+			*step = 1;
+			return '[';
+		}
+		*step = k+1;
+		return BRACKET;
+	}
+	if (pat[0] == '*')
+		return STAR;
+	if (pat[0] == '?')
+		return QUESTION;
+escaped:
+	if (pat[0] >= 128U) {
+		wchar_t wc;
+		int k = mbtowc(&wc, pat, m);
+		if (k<0) {
+			*step = 0;
+			return UNMATCHABLE;
+		}
+		*step = k + esc;
+		return wc;
 	}
-	c = next(s);
-	if (c <= 0) return BRACKET_ERROR;
-	return c;
+	return pat[0];
 }
 
-#define __FNM_CONT 0x8000
+static int match_bracket(const char *p, int k)
+{
+	wchar_t wc;
+	int inv = 0;
+	p++;
+	if (*p=='^' || *p=='!') {
+		inv = 1;
+		p++;
+	}
+	if (*p==']') {
+		if (k==']') return !inv;
+		p++;
+	} else if (*p=='-') {
+		if (k=='-') return !inv;
+		p++;
+	}
+	wc = p[-1];
+	for (; *p != ']'; p++) {
+		if (p[0]=='-' && p[1]!=']') {
+			wchar_t wc2;
+			int l = mbtowc(&wc2, p+1, 4);
+			if (l < 0) return 0;
+			if (wc<=wc2 && (unsigned)k-wc <= wc2-wc) return !inv;
+			p += l-1;
+			continue;
+		}
+		if (p[0]=='[' && (p[1]==':' || p[1]=='.' || p[1]=='=')) {
+			const char *p0 = p+2;
+			int z = p[1];
+			p+=3;
+			while (p[-1]!=z || p[0]!=']') p++;
+			if (z == ':' && p-1-p0 < 16) {
+				char buf[16];
+				memcpy(buf, p0, p-1-p0);
+				buf[p-1-p0] = 0;
+				if (iswctype(k, wctype(buf))) return !inv;
+			}
+			continue;
+		}
+		if (*p < 128U) {
+			wc = (unsigned char)*p;
+		} else {
+			int l = mbtowc(&wc, p, 4);
+			if (l < 0) return 0;
+			p += l-1;
+		}
+		if (wc==k) return !inv;
+	}
+	return inv;
+}
 
-int fnmatch(const char *p, const char *s, int flags)
+static int fnmatch_internal(const char *pat, size_t m, const char *str, size_t n, int flags)
 {
-	int c, d, k;
-	int not;
-	int match;
-	int first;
-	int no_slash = (flags & FNM_PATHNAME) ? '/' : 0;
-	int no_period = (flags & FNM_PERIOD) && !(flags & __FNM_CONT) ? '.' : 0x100;
-	const char *p1;
-
-	flags |= __FNM_CONT;
-
-	while ((c = *p++)) {
-		switch (c) {
-		case '?':
-			k = next(&s);
-			if (!k || k == no_period || k == no_slash)
-				return FNM_NOMATCH;
+	const char *p, *ptail, *endpat;
+	const char *s, *stail, *endstr;
+	size_t pinc, sinc, tailcnt=0;
+	int c, k;
+
+	if (flags & FNM_PERIOD) {
+		if (*str == '.' && *pat != '.')
+			return FNM_NOMATCH;
+	}
+	for (;;) {
+		switch ((c = pat_next(pat, m, &pinc, flags))) {
+		case UNMATCHABLE:
+			return FNM_NOMATCH;
+		case STAR:
+			pat++;
+			m--;
 			break;
-		case '\\':
-			if (!(flags & FNM_NOESCAPE)) {
-				c = *p++;
-				goto literal;
+		default:
+			k = str_next(str, n, &sinc);
+			if (k <= 0)
+				return (c==END) ? 0 : FNM_NOMATCH;
+			str += sinc;
+			n -= sinc;
+			if (c == BRACKET) {
+				if (!match_bracket(pat, k))
+					return FNM_NOMATCH;
+			} else if (c != QUESTION && k != c) {
+				return FNM_NOMATCH;
 			}
-			if (*s++ != c) return FNM_NOMATCH;
+			pat+=pinc;
+			m-=pinc;
+			continue;
+		}
+		break;
+	}
+
+	/* Compute real pat length if it was initially unknown/-1 */
+	m = strnlen(pat, m);
+	endpat = pat + m;
+
+	/* Find the last * in pat and count chars needed after it */
+	for (p=ptail=pat; p<endpat; p+=pinc) {
+		switch (pat_next(p, endpat-p, &pinc, flags)) {
+		case UNMATCHABLE:
+			return FNM_NOMATCH;
+		case STAR:
+			tailcnt=0;
+			ptail = p+1;
 			break;
-		case '*':
-			for (; *p == '*'; p++);
-			if (*p && !*s) return FNM_NOMATCH;
-			if (*s == no_period)
+		default:
+			tailcnt++;
+			break;
+		}
+	}
+
+	/* Past this point we need not check for UNMATCHABLE in pat,
+	 * because all of pat has already been parsed once. */
+
+	/* Compute real str length if it was initially unknown/-1 */
+	n = strnlen(str, n);
+	endstr = str + n;
+	if (n < tailcnt) return FNM_NOMATCH;
+
+	/* Find the final tailcnt chars of str, accounting for UTF-8.
+	 * On illegal sequences we may get it wrong, but in that case
+	 * we necessarily have a matching failure anyway. */
+	for (s=endstr; s>str && tailcnt; tailcnt--) {
+		if (s[-1] < 128U) s--;
+		else while ((unsigned char)*--s-0x80U<0x40 && s>str);
+	}
+	if (tailcnt) return FNM_NOMATCH;
+	stail = s;
+
+	/* Check that the pat and str tails match */
+	p = ptail;
+	for (;;) {
+		c = pat_next(p, endpat-p, &pinc, flags);
+		p += pinc;
+		if ((k = str_next(s, endstr-s, &sinc)) <= 0) {
+			if (c != END) return FNM_NOMATCH;
+			break;
+		}
+		s += sinc;
+		if (c == BRACKET) {
+			if (!match_bracket(p-pinc, k))
 				return FNM_NOMATCH;
-			if (!*p && (!no_slash || !strchr(s, no_slash)))
-				return 0;
-			for (; *s; s++)
-				if (!fnmatch(p, s, flags))
-					return 0;
-				else if (*s == no_slash)
-					break;
+		} else if (c != QUESTION && k != c) {
 			return FNM_NOMATCH;
-		case '[':
-			p1 = p-1;
-			not = (*p == '!' || *p == '^');
-			if (not) p++;
-			k = next(&s);
-			if (!k || k == no_slash || k == no_period)
-				return FNM_NOMATCH;
-			match = 0;
-			first = 1;
-			for (;;) {
-				if (!*p) goto literal_bracket;
-				if (*p == ']' && !first) break;
-				first = 0;
-				if (*p == '[' && *(p+1) == ':') {
-					const char *z;
-					p += 2;
-					for (z=p; *z && (*z != ':' || *(z+1) != ']'); z++);
-					if (!*z || z-p > 32) { /* FIXME: symbolic const? */
-						return FNM_NOMATCH;
-					} else {
-						char class[33];
-						memcpy(class, p, z-p);
-						class[z-p] = 0;
-						if (iswctype(k, wctype(class)))
-							match = 1;
-					}
-					p = z+2;
-					continue;
-				}
-				c = bracket_next(&p);
-				if (c == BRACKET_ERROR) {
-literal_bracket:
-					match = (k=='[');
-					p = p1;
-					not = 0;
-					break;
-				}
-				if (c == BRACKET_NOCHAR)
-					continue;
-				if (*p == '-' && *(p+1) != ']') {
-					p++;
-					d = bracket_next(&p);
-					if (d == BRACKET_ERROR)
-						goto literal_bracket;
-					if (d == BRACKET_NOCHAR)
-						continue;
-					if (k >= c && k <= d)
-						match = 1;
-					continue;
-				}
-				if (k == c) match = 1;
+		}
+	}
+
+	/* We're all done with the tails now, so throw them out */
+	endstr = stail;
+	endpat = ptail;
+
+	/* Match pattern components until there are none left */
+	while (pat<endpat) {
+		p = pat;
+		s = str;
+		for (;;) {
+			c = pat_next(p, endpat-p, &pinc, flags);
+			p += pinc;
+			/* Encountering * completes/commits a component */
+			if (c == STAR) {
+				pat = p;
+				str = s;
+				break;
 			}
-			p++;
-			if (not == match)
+			k = str_next(s, endstr-s, &sinc);
+			if (!k)
 				return FNM_NOMATCH;
-			break;
-		default:
-		literal:
-			if (*s++ != c)
-				return FNM_NOMATCH;
-			if (c == no_slash && (flags & FNM_PERIOD)) {
-				no_period = '.';
-				continue;
+			if (c == BRACKET) {
+				if (!match_bracket(p-pinc, k))
+					break;
+			} else if (c != QUESTION && k != c) {
+				break;
 			}
-			break;
+			s += sinc;
 		}
-		no_period = 0x100;
+		if (c == STAR) continue;
+		/* If we failed, advance str, by 1 char if it's a valid
+		 * char, or past all invalid bytes otherwise. */
+		k = str_next(str, endstr-str, &sinc);
+		if (k > 0) str += sinc;
+		else for (str++; str_next(str, endstr-str, &sinc)<0; str++);
 	}
-	if (*s) return FNM_NOMATCH;
+
 	return 0;
 }
+
+int fnmatch(const char *pat, const char *str, int flags)
+{
+	const char *s, *p;
+	size_t inc;
+	int c;
+	if (flags & FNM_PATHNAME) for (;;) {
+		for (s=str; *s && *s!='/'; s++);
+		for (p=pat; (c=pat_next(p, -1, &inc, flags))!=END && c!='/'; p+=inc);
+		if (*s && *p!=*s) return FNM_NOMATCH;
+		if (fnmatch_internal(pat, p-pat, str, s-str, flags))
+			return FNM_NOMATCH;
+		if (!*s && c==END) return 0;
+		str = s+1;
+		pat = p+1;
+	}
+	return fnmatch_internal(pat, -1, str, -1, flags);
+}