linux-kernel - [PATCH] memchr (trivial) optimization

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Message-ID: <BAY105-F323FF3DC8E6C544A2BBE98FFD50@phx.gbl>
Date:	Wed, 22 Aug 2007 11:34:49 +0200
From:	"lode leroy" <lode_leroy@...mail.com>
To:	linux-kernel@...r.kernel.org
Subject: [PATCH] memchr (trivial) optimization

While profiling something completely unrelated, I noticed
that on the workloads I used memchr for, I saw a 30%-40% improvement
in performance, with the following trivial changes...
(basically, it saves 3 operations for each call)

$ diff -Nurp linux/lib/string.c{-old,}
--- linux/lib/string.c-old      2007-08-22 11:18:54.000000000 +0200
+++ linux/lib/string.c  2007-08-22 11:19:20.000000000 +0200
@@ -623,10 +623,12 @@ EXPORT_SYMBOL(strstr);
void *memchr(const void *s, int c, size_t n)
{
        const unsigned char *p = s;
-       while (n-- != 0) {
-               if ((unsigned char)c == *p++) {
-                       return (void *)(p - 1);
+       while (n != 0) {
+               if ((unsigned char)c == *p) {
+                       return (void *)p;
                }
+               n--;
+               p++;
        }
        return NULL;
}

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