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 af9fffe6e8e145b066157da8791c749257e7c8e9..574b3e833711fe3794636b86dbf2b9d9deb5e151 100644 (file)
--- 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);