git/compat
René Scharfe 56384e61ea 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>
2009-03-02 18:28:06 -08:00
..
fnmatch Use compatibility regex library for OSX/Darwin 2008-09-10 13:36:40 -07:00
regex Use compatibility regex library for OSX/Darwin 2008-09-10 13:36:40 -07:00
cygwin.c compat/cygwin.c: make runtime detection of lstat/stat lessor impact 2008-10-28 09:12:49 -07:00
cygwin.h cygwin: Use native Win32 API for stat 2008-09-30 14:30:06 -07:00
fopen.c compat/fopen.c: avoid clobbering the system defined fopen macro 2008-05-08 17:43:01 -07:00
hstrerror.c Add a local implementation of hstrerror for the system which do not have it 2007-06-15 22:48:34 -07:00
inet_ntop.c Remove a couple of duplicated include 2007-11-05 20:50:38 -08:00
inet_pton.c Remove a couple of duplicated include 2007-11-05 20:50:38 -08:00
memmem.c optimize compat/ memmem() 2009-03-02 18:28:06 -08:00
mingw.c Merge branch 'js/mingw-rename-fix' 2008-11-27 19:25:06 -08:00
mingw.h Windows: Fix signal numbers 2009-01-21 22:46:52 -08:00
mkdtemp.c Define compat version of mkdtemp for systems lacking it 2007-10-20 22:52:21 -04:00
mmap.c War on whitespace 2007-06-07 00:04:01 -07:00
pread.c Replacing the system call pread() with lseek()/xread()/lseek() sequence. 2007-01-09 16:40:40 -08:00
qsort.c compat: Add simplified merge sort implementation from glibc 2008-02-06 22:35:28 -08:00
setenv.c simplify inclusion of system header files. 2006-12-20 09:51:35 -08:00
snprintf.c compat/snprintf.c: handle snprintf's that always return the # chars transmitted 2008-08-21 01:53:44 -07:00
strcasestr.c Clean up compatibility definitions. 2005-12-05 15:50:29 -08:00
strlcpy.c simplify inclusion of system header files. 2006-12-20 09:51:35 -08:00
strtoumax.c Add a compat/strtoumax.c for Solaris 8. 2007-02-19 18:20:30 -08:00
unsetenv.c simplify inclusion of system header files. 2006-12-20 09:51:35 -08:00
win32.h mingw: move common functionality to win32.h 2008-09-30 14:30:06 -07:00
winansi.c Add ANSI control code emulation for the Windows console 2008-07-19 11:17:43 -07:00