From ce163c793d2058056ccc57563c350fd6415397ca Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ren=C3=A9=20Scharfe?= <rene.scharfe@lsrfire.ath.cx>
Date: Tue, 3 Mar 2009 00:00:55 +0100
Subject: diffcore-pickaxe: use memmem()

Use memmem() instead of open-coding it.  The system libraries usually have a
much faster version than the memcmp()-loop here.  Even our own fall-back in
compat/, which is used on Windows, is slightly faster.

The following commands were run in a Linux kernel repository and timed, the
best of five results is shown:

  $ STRING='Ensure that the real time constraints are schedulable.'
  $ git log -S"$STRING" HEAD -- kernel/sched.c >/dev/null

On Ubuntu 8.10 x64, before (v1.6.2-rc2):

  8.09user 0.04system 0:08.14elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
  0inputs+0outputs (0major+30952minor)pagefaults 0swaps

And with the patch:

  1.50user 0.04system 0:01.54elapsed 100%CPU (0avgtext+0avgdata 0maxresident)k
  0inputs+0outputs (0major+30645minor)pagefaults 0swaps

On Fedora 10 x64, before:

  8.34user 0.05system 0:08.39elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
  0inputs+0outputs (0major+29268minor)pagefaults 0swaps

And with the patch:

  1.15user 0.05system 0:01.20elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
  0inputs+0outputs (0major+32253minor)pagefaults 0swaps

On Windows Vista x64, before:

  real    0m9.204s
  user    0m0.000s
  sys     0m0.000s

And with the patch:

  real    0m8.470s
  user    0m0.000s
  sys     0m0.000s

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/diffcore-pickaxe.c b/diffcore-pickaxe.c
index af9fffe..574b3e8 100644
--- a/diffcore-pickaxe.c
+++ b/diffcore-pickaxe.c
@@ -10,7 +10,7 @@ static unsigned int contains(struct diff_filespec *one,
 			     regex_t *regexp)
 {
 	unsigned int cnt;
-	unsigned long offset, sz;
+	unsigned long sz;
 	const char *data;
 	if (diff_populate_filespec(one, 0))
 		return 0;
@@ -33,15 +33,13 @@ static unsigned int contains(struct diff_filespec *one,
 		}
 
 	} else { /* Classic exact string match */
-		/* Yes, I've heard of strstr(), but the thing is *data may
-		 * not be NUL terminated.  Sue me.
-		 */
-		for (offset = 0; offset + len <= sz; offset++) {
-			/* we count non-overlapping occurrences of needle */
-			if (!memcmp(needle, data + offset, len)) {
-				offset += len - 1;
-				cnt++;
-			}
+		while (sz) {
+			const char *found = memmem(data, sz, needle, len);
+			if (!found)
+				break;
+			sz -= found - data + len;
+			data = found + len;
+			cnt++;
 		}
 	}
 	diff_free_filespec_data(one);
-- 
cgit v0.10.2-6-g49f6


From 56384e61ead8d41c39bfafb535eedcf67ef4fcc3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ren=C3=A9=20Scharfe?= <rene.scharfe@lsrfire.ath.cx>
Date: Tue, 3 Mar 2009 00:19:30 +0100
Subject: optimize compat/ memmem()

When memmem() was imported from glibc 2.2 into compat/, an optimization
was dropped in the process, in order to make the code smaller and simpler.
It was OK because memmem() wasn't used in performance-critical code.  Now
the situation has changed and we can benefit from this optimization.

The trick is to avoid calling memcmp() if the first character of the needle
already doesn't match.  Checking one character directly is much cheaper
than the function call overhead.  We keep the first character of the needle
in the variable named point and the rest in the one named tail.

The following commands were run in a Linux kernel repository and timed, the
best of five results is shown:

  $ STRING='Ensure that the real time constraints are schedulable.'
  $ git log -S"$STRING" HEAD -- kernel/sched.c >/dev/null

On Windows Vista x64, before:

  real    0m8.470s
  user    0m0.000s
  sys     0m0.000s

And after the patch:

  real    0m1.887s
  user    0m0.000s
  sys     0m0.000s

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/compat/memmem.c b/compat/memmem.c
index cd0d877..56bcb42 100644
--- a/compat/memmem.c
+++ b/compat/memmem.c
@@ -5,6 +5,8 @@ void *gitmemmem(const void *haystack, size_t haystack_len,
 {
 	const char *begin = haystack;
 	const char *last_possible = begin + haystack_len - needle_len;
+	const char *tail = needle;
+	char point;
 
 	/*
 	 * The first occurrence of the empty string is deemed to occur at
@@ -20,8 +22,9 @@ void *gitmemmem(const void *haystack, size_t haystack_len,
 	if (haystack_len < needle_len)
 		return NULL;
 
+	point = *tail++;
 	for (; begin <= last_possible; begin++) {
-		if (!memcmp(begin, needle, needle_len))
+		if (*begin == point && !memcmp(begin + 1, tail, needle_len - 1))
 			return (void *)begin;
 	}
 
-- 
cgit v0.10.2-6-g49f6