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git_oid_cmp: inline memcmp by hand to optimize

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git.git uses an inlined hashcmp function instead of memcmp, since it
performes much better when comparing hashes (most hashes compared
diverge within the first byte).

Measurements and rationale for the curious reader:
http://thread.gmane.org/gmane.comp.version-control.git/172286
This commit is contained in:
Michael Schubert 2012-07-27 10:53:09 +02:00
parent 6810ba089a
commit f6b26e770f
3 changed files with 26 additions and 12 deletions
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26
include/git2/oid.h
View File

@ -136,7 +136,31 @@ GIT_EXTERN(void) git_oid_cpy(git_oid *out, const git_oid *src);
* @param b second oid structure.
* @return <0, 0, >0 if a < b, a == b, a > b.
*/
GIT_EXTERN(int) git_oid_cmp(const git_oid *a, const git_oid *b);
GIT_INLINE(int) git_oid_cmp(const git_oid *a, const git_oid *b)
{
const unsigned char *sha1 = a->id;
const unsigned char *sha2 = b->id;
int i;
for (i = 0; i < GIT_OID_RAWSZ; i++, sha1++, sha2++) {
if (*sha1 != *sha2)
return *sha1 - *sha2;
}
return 0;
}
/**
* Compare two oid structures for equality
*
* @param a first oid structure.
* @param b second oid structure.
* @return true if equal, false otherwise
*/
GIT_INLINE(int) git_oid_equal(const git_oid *a, const git_oid *b)
{
return !git_oid_cmp(a, b);
}
/**
* Compare the first 'len' hexadecimal characters (packets of 4 bits)

5
src/oid.c
View File

@ -161,11 +161,6 @@ void git_oid_cpy(git_oid *out, const git_oid *src)
memcpy(out->id, src->id, sizeof(out->id));
}
int git_oid_cmp(const git_oid *a, const git_oid *b)
{
return memcmp(a->id, b->id, sizeof(a->id));
}
int git_oid_ncmp(const git_oid *oid_a, const git_oid *oid_b, unsigned int len)
{
const unsigned char *a = oid_a->id;

7
src/oidmap.h
View File

@ -28,13 +28,8 @@ GIT_INLINE(khint_t) hash_git_oid(const git_oid *oid)
return h;
}
GIT_INLINE(int) hash_git_oid_equal(const git_oid *a, const git_oid *b)
{
return (memcmp(a->id, b->id, sizeof(a->id)) == 0);
}
#define GIT__USE_OIDMAP \
__KHASH_IMPL(oid, static kh_inline, const git_oid *, void *, 1, hash_git_oid, hash_git_oid_equal)
__KHASH_IMPL(oid, static kh_inline, const git_oid *, void *, 1, hash_git_oid, git_oid_equal)
#define git_oidmap_alloc() kh_init(oid)
#define git_oidmap_free(h) kh_destroy(oid,h), h = NULL