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, 40 insertions, 24 deletions

diff --git a/sys/libkern/strspn.c b/sys/libkern/strspn.c
index 6bcdeca..18327b7 100644
--- a/sys/libkern/strspn.c
+++ b/sys/libkern/strspn.c
@@ -1,6 +1,6 @@
-/*
- * Copyright (c) 1989, 1993
- *	The Regents of the University of California.  All rights reserved.
+/*-
+ * 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
@@ -10,14 +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.
- * 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)
@@ -31,25 +28,44 @@
 __FBSDID("$FreeBSD$");
 
 #include <sys/libkern.h>
+#include <sys/limits.h>
+#include <sys/types.h>
+
+#define	IDX(c)	((u_char)(c) / LONG_BIT)
+#define	BIT(c)	((u_long)1 << ((u_char)(c) % LONG_BIT))
 
-/*
- * Span the string s2 (skip characters that are in s2).
- */
 size_t
-strspn(s1, s2)
-	const char *s1;
-	const char *s2;
+strspn(const char *s, const char *charset)
 {
-	const char *p = s1, *spanp;
-	char c, sc;
-
 	/*
-	 * Skip any characters in s2, excluding the terminating \0.
+	 * NB: idx and bit are temporaries whose use causes gcc 3.4.2 to
+	 * generate better code.  Without them, gcc gets a little confused.
 	 */
-cont:
-	c = *p++;
-	for (spanp = s2; (sc = *spanp++) != 0;)
-		if (sc == c)
-			goto cont;
-	return (p - 1 - s1);
+	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[3] = tbl[2] = tbl[1] = tbl[0] = 0;
+#else
+	for (idx = 0; 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;
+	}
+	return (s1 - s);
 }