optimize strchrnul/strcspn not to scan string twice on no-match

when strchr fails, and important piece of information already
computed, the string length, is thrown away. have strchrnul (with
namespace protection) be the underlying function so this information
can be kept, and let strchr be a wrapper for it. this also allows
strcspn to be considerably faster in the case where the match set has
a single element that's not matched.

1 files changed, 23 insertions, 3 deletions

diff --git a/src/string/strchrnul.c b/src/string/strchrnul.c
index 5e0c1a1a..ceae4d45 100644
--- a/src/string/strchrnul.c
+++ b/src/string/strchrnul.c
@@ -1,7 +1,27 @@
 #include <string.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <limits.h>
+#include "libc.h"
 
-char *strchrnul(const char *s, int c)
+#define ALIGN (sizeof(size_t))
+#define ONES ((size_t)-1/UCHAR_MAX)
+#define HIGHS (ONES * (UCHAR_MAX/2+1))
+#define HASZERO(x) ((x)-ONES & ~(x) & HIGHS)
+
+char *__strchrnul(const char *s, int c)
 {
-	char *p = strchr(s, c);
-	return p ? p : (char *)s + strlen(s);
+	size_t *w, k;
+
+	c = (unsigned char)c;
+	if (!c) return (char *)s + strlen(s);
+
+	for (; (uintptr_t)s % ALIGN; s++)
+		if (!*s || *(unsigned char *)s == c) return (char *)s;
+	k = ONES * c;
+	for (w = (void *)s; !HASZERO(*w) && !HASZERO(*w^k); w++);
+	for (s = (void *)w; *s && *(unsigned char *)s != c; s++);
+	return (char *)s;
 }
+
+weak_alias(__strchrnul, strchrnul);