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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>

authored by

René Scharfe and committed by
Junio C Hamano ce163c79 f474c526

+8 -10
unified split
+8 -10
diffcore-pickaxe.c
··· 10 regex_t *regexp) 11 { 12 unsigned int cnt; 13 - unsigned long offset, sz; 14 const char *data; 15 if (diff_populate_filespec(one, 0)) 16 return 0; ··· 33 } 34 35 } else { /* Classic exact string match */ 36 - /* Yes, I've heard of strstr(), but the thing is *data may 37 - * not be NUL terminated. Sue me. 38 - */ 39 - for (offset = 0; offset + len <= sz; offset++) { 40 - /* we count non-overlapping occurrences of needle */ 41 - if (!memcmp(needle, data + offset, len)) { 42 - offset += len - 1; 43 - cnt++; 44 - } 45 } 46 } 47 diff_free_filespec_data(one);
··· 10 regex_t *regexp) 11 { 12 unsigned int cnt; 13 + unsigned long sz; 14 const char *data; 15 if (diff_populate_filespec(one, 0)) 16 return 0; ··· 33 } 34 35 } else { /* Classic exact string match */ 36 + while (sz) { 37 + const char *found = memmem(data, sz, needle, len); 38 + if (!found) 39 + break; 40 + sz -= found - data + len; 41 + data = found + len; 42 + cnt++; 43 } 44 } 45 diff_free_filespec_data(one);