From: Rajalakshmi Srinivasaraghavan <raji@linux.vnet.ibm.com>
Date: Tue, 28 Aug 2018 07:12:19 +0000 (+0530)
Subject: Speedup first memmem match
X-Git-Tag: glibc-2.29~490
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c8dd67e7c958de04c3783cbea7c384431707b5f8;p=thirdparty%2Fglibc.git

Speedup first memmem match

As done in commit 284f42bc778e487dfd5dff5c01959f93b9e0c4f5, memcmp
can be used after memchr to avoid the initialization overhead of the
two-way algorithm for the first match.  This has shown improvement
>40% for first match.
---

diff --git a/ChangeLog b/ChangeLog
index 8419d4671c4..2a250970e43 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2018-08-28  Rajalakshmi Srinivasaraghavan  <raji@linux.vnet.ibm.com>
+
+	* string/memmem.c: Use memcmp for first match.
+
 2018-08-28  Rafal Luzynski  <digitalfreak@lingonborough.com>
 
 	[BZ #17426]
diff --git a/string/memmem.c b/string/memmem.c
index 43efaa3fb71..d72b8249e62 100644
--- a/string/memmem.c
+++ b/string/memmem.c
@@ -70,6 +70,10 @@ __memmem (const void *haystack_start, size_t haystack_len,
       haystack_len -= haystack - (const unsigned char *) haystack_start;
       if (haystack_len < needle_len)
 	return NULL;
+      /* Check whether we have a match.  This improves performance since we
+	 avoid the initialization overhead of the two-way algorithm.  */
+      if (memcmp (haystack, needle, needle_len) == 0)
+	return (void *) haystack;
       return two_way_short_needle (haystack, haystack_len, needle, needle_len);
     }
   else