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mdbx: refine/speedup mdb_cmp_memn().

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Change-Id: I2c62246b26485039f29bc400a4d42f05270a7398
This commit is contained in:
Leo Yuriev 2016-04-27 12:16:17 +03:00
parent 477932e2b3
commit 78e6bf5e36
1 changed files with 16 additions and 3 deletions
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19
mdb.c
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@ -5237,9 +5237,22 @@ mdb_cmp_int_ua(const MDB_val *a, const MDB_val *b)
static int __hot
mdb_cmp_memn(const MDB_val *a, const MDB_val *b)
{
size_t minlen = (a->mv_size < b->mv_size) ? a->mv_size : b->mv_size;
int diff = memcmp(a->mv_data, b->mv_data, minlen);
return likely(diff) ? diff : mdbx_cmp2int(a->mv_size, b->mv_size);
/* LY: assumes that length of keys are NOT equal for most cases,
* if no then branch-prediction should mitigate the problem */
#if 0
/* LY: without branch instructions on x86,
* but isn't best for equal length of keys */
int diff_len = mdbx_cmp2int(a->mv_size, b->mv_size);
#else
/* LY: best when length of keys are equal,
* but got a branch-penalty otherwise */
if (unlikely(a->mv_size == b->mv_size))
return memcmp(a->mv_data, b->mv_data, a->mv_size);
int diff_len = (a->mv_size < b->mv_size) ? -1 : 1;
#endif
size_t shortest = (a->mv_size < b->mv_size) ? a->mv_size : b->mv_size;
int diff_data = memcmp(a->mv_data, b->mv_data, shortest);
return likely(diff_data) ? diff_data : diff_len;
}
/** Compare two items in reverse byte order */