Compare strings by SSE4 wrappers

Question

I need to quickly compare two string on the machine with SSE4 support. How can I do it without writing assembler inserts?

Some wrappers like long long bitmask = strcmp(char* a, char* b) would be perfect.

it might depend on the compiler (including the version) and the flags used. If you use `gcc-4.7` did you try `-mcpu=native -O3` etc.? — Basile Starynkevitch, May 13 '12 at 20:21
http://software.intel.com/sites/products/documentation/studio/composer/en-us/2011/compiler_c/intref_cls/common/intref_sse42_comp.htm — Mysticial, May 13 '12 at 20:22
Googling "sse4 strcmp" gives a lot of results with ready made assembler code. You can try to translate those to C using intrinsics. Have fun. — Gunther Piez, May 13 '12 at 20:38

Mysticial · Accepted Answer · 2013-01-28T23:53:02.007

9

Instead of using inline assembly, you should use the Intel SSE intrinsics.

For string comparison, you'll need the SSE4.2 intrinsics:

Documentation is here: http://software.intel.com/sites/products/documentation/doclib/stdxe/2013/composerxe/compiler/cpp-mac/GUID-6E9CFDF2-5DF6-42A4-B429-0E2CD441342E.htm

edited Jan 28 '13 at 23:53

answered May 13 '12 at 21:07

Mysticial

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And you are correct. They changed the link. Updated with the new one. – Mysticial Jan 28 '13 at 23:53
Note that SSE4.2 instructions are generally *not* worth using for strcmp or strlen. You can do better with SSE2 or especially AVX2, which is what glibc does in practice. See links at the top of [my answer on Why does glibc's strlen need to be so complicated to run quickly?](https://stackoverflow.com/a/57676035) (That question is about glibc's fallback C implementation, which is never used on x86.) – Peter Cordes Oct 26 '20 at 06:14

score 2 · Answer 2 · answered Jun 03 '13 at 14:05

Use Agner Fog's asmlib. http://www.agner.org/optimize/#asmlib

He's already taken the trouble for writing the code in assembly for you including using SSE4.2 instructions. Use his function A_strcmp (or the case insensitive version A_stricmp).

It would be interesting so how a method using intrinsics compares in performance.

score 0 · Answer 3 · answered Jun 03 '13 at 07:42

0

Here is a good article of using SSE 4.2 for boosting string operations: http://www.strchr.com/strcmp_and_strlen_using_sse_4.2

answered Jun 03 '13 at 07:42

Hang Su

1

Compare strings by SSE4 wrappers

3 Answers3