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Author	SHA1	Message	Date
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>	16 years ago
René Scharfe	b21b9f1de3	add memmem() memmem() is a nice GNU extension for searching a length limited string in another one. This compat version is based on the version found in glibc 2.2 (GPL 2); I only removed the optimization of checking the first char by hand, and generally tried to keep the code simple. We can add it back if memcmp shows up high in a profile, but for now I prefer to keep it (almost trivially) simple. Since I don't really know which platforms beside those with a glibc have their own memmem(), I used a heuristic: if NO_STRCASESTR is set, then NO_MEMMEM is set, too. Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx> Signed-off-by: Junio C Hamano <gitster@pobox.com>	18 years ago

Author

SHA1

Message

Date

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>

16 years ago

René Scharfe

b21b9f1de3

add memmem()

memmem() is a nice GNU extension for searching a length limited string
in another one.

This compat version is based on the version found in glibc 2.2 (GPL 2);
I only removed the optimization of checking the first char by hand, and
generally tried to keep the code simple.  We can add it back if memcmp
shows up high in a profile, but for now I prefer to keep it (almost
trivially) simple.

Since I don't really know which platforms beside those with a glibc
have their own memmem(), I used a heuristic: if NO_STRCASESTR is set,
then NO_MEMMEM is set, too.

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

18 years ago

2 Commits (dd0d388c44c28ebc021a24eeddc60287d4ea249c)