[PATCH] Improve memmem.

[Ondřej Bílka]

Hi.

This is same optimization for memmem as for strstr.
On x64 memmem performance sucks as its order of magnitude slower than strstr.
This equalizes performance somewhat and improves it in general case.

OK to commit this?


diff --git a/string/memmem.c b/string/memmem.c
index 8a81f65..ed21ee4 100644
--- a/string/memmem.c
+++ b/string/memmem.c
@@ -46,6 +46,10 @@ __memmem (const void *haystack_start, size_t haystack_len,
      not an array of 'char' values.  See ISO C 99 section 6.2.6.1.  */
   const unsigned char *haystack = (const unsigned char *) haystack_start;
   const unsigned char *needle = (const unsigned char *) needle_start;
+  const unsigned char *haystack_end = (const unsigned char *) 
+				      haystack_start + haystack_len 
+				      - needle_len + 1;
+
 
    if (needle_len == 0)
      /* The first occurrence of the empty string is deemed to occur at
@@ -57,6 +61,29 @@ __memmem (const void *haystack_start, size_t haystack_len,
   if (__glibc_unlikely (haystack_len < needle_len))
     return NULL;
 
+  if (needle_len == 1)
+    return memchr (haystack, needle[0], haystack_end - haystack);
+
+  while ((haystack = memchr (haystack, needle[0], haystack_end - haystack)))
+    {
+      if (haystack[1] == needle[1] 
+          && (needle_len == 2 || haystack[2] == needle[2]))
+        {
+          if (needle_len == 2)
+            return haystack;
+
+          if (!memcmp (haystack + 2, needle + 2, needle_len - 2))
+            return haystack;
+          else  
+            goto slow_path;
+        }
+      haystack++;
+    }
+
+  return NULL;
+
+  slow_path:;
+
   /* Use optimizations in memchr when possible, to reduce the search
      size of haystack using a linear algorithm with a smaller
      coefficient.  However, avoid memchr for long needles, since we