Replace the current strspn() and strcspn() with significantly faster

implementations inspired by the ones in DragonFly.  Unlike the
DragonFly versions, these have a small data cache footprint, and my
tests show that they're never slower than the old code except when the
charset or the span is 0 or 1 characters.  This implementation is
generally faster than DragonFly until either the charset or the span
gets in the ballpark of 32 to 64 characters.

1 files changed, 39 insertions, 36 deletions

diff --git a/lib/libc/string/strcspn.c b/lib/libc/string/strcspn.c
index 2ec9326..3879a3b 100644
--- a/lib/libc/string/strcspn.c
+++ b/lib/libc/string/strcspn.c
@@ -1,9 +1,6 @@
 /*-
- * Copyright (c) 1990, 1993
- *	The Regents of the University of California.  All rights reserved.
- *
- * This code is derived from software contributed to Berkeley by
- * Chris Torek.
+ * Copyright (c) 2005 David Schultz <das@FreeBSD.ORG>
+ * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -13,18 +10,11 @@
  * 2. 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.
- * 3. All advertising materials mentioning features or use of this software
- *    must display the following acknowledgement:
- *	This product includes software developed by the University of
- *	California, Berkeley and its contributors.
- * 4. Neither the name of the University 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 REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 REGENTS OR CONTRIBUTORS BE LIABLE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR 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)
@@ -34,36 +24,49 @@
  * SUCH DAMAGE.
  */
 
-#if defined(LIBC_SCCS) && !defined(lint)
-static char sccsid[] = "@(#)strcspn.c	8.1 (Berkeley) 6/4/93";
-#endif /* LIBC_SCCS and not lint */
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
+#include <sys/types.h>
+#include <limits.h>
 #include <string.h>
 
-/*
- * Span the complement of string s2.
- */
+#define	IDX(c)	((u_char)(c) / LONG_BIT)
+#define	BIT(c)	((u_long)1 << ((u_char)(c) % LONG_BIT))
+
 size_t
-strcspn(s1, s2)
-	const char *s1;
-	const char *s2;
+strcspn(const char *s, const char *charset)
 {
-	const char *p, *spanp;
-	char c, sc;
-
 	/*
-	 * Stop as soon as we find any character from s2.  Note that there
-	 * must be a NUL in s2; it suffices to stop when we find that, too.
+	 * NB: idx and bit are temporaries whose use causes gcc 3.4.2 to
+	 * generate better code.  Without them, gcc gets a little confused.
 	 */
-	for (p = s1;;) {
-		c = *p++;
-		spanp = s2;
-		do {
-			if ((sc = *spanp++) == c)
-				return (p - 1 - s1);
-		} while (sc != 0);
+	const char *s1;
+	u_long bit;
+	u_long tbl[(UCHAR_MAX + 1) / LONG_BIT];
+	int idx;
+
+	if(*s == '\0')
+		return (0);
+
+#if LONG_BIT == 64	/* always better to unroll on 64-bit architectures */
+	tbl[0] = 1;
+	tbl[3] = tbl[2] = tbl[1] = 0;
+#else
+	for (tbl[0] = idx = 1; idx < sizeof(tbl) / sizeof(tbl[0]); idx++)
+		tbl[idx] = 0;
+#endif
+	for (; *charset != '\0'; charset++) {
+		idx = IDX(*charset);
+		bit = BIT(*charset);
+		tbl[idx] |= bit;
+	}
+
+	for(s1 = s; ; s1++) {
+		idx = IDX(*s1);
+		bit = BIT(*s1);
+		if ((tbl[idx] & bit) != 0)
+			break;
 	}
-	/* NOTREACHED */
+	return (s1 - s);
 }