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MINOR: tools/rnd: compute the result outside of the CAS loop

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ha_random64() uses a DWCAS loop to produce the random, but it computes
the resulting value inside the loop while it doesn't change upon success,
so this is a needless overhead inside the critcal path that participates
to making threads fail the race and try again. Let's take the value out
of the loop.
This commit is contained in:
Willy Tarreau 2021-05-09 10:26:14 +02:00
parent 714f34580e
commit b2475a139e
1 changed files with 1 additions and 3 deletions
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4
src/tools.c
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@ -5021,7 +5021,6 @@ static uint64_t ha_random_state[2] ALIGNED(2*sizeof(uint64_t));
*/
uint64_t ha_random64()
{
uint64_t result;
uint64_t old[2] ALIGNED(2*sizeof(uint64_t));
uint64_t new[2] ALIGNED(2*sizeof(uint64_t));
@ -5037,7 +5036,6 @@ uint64_t ha_random64()
#if defined(USE_THREAD) && defined(HA_CAS_IS_8B) && defined(HA_HAVE_CAS_DW)
do {
#endif
result = rotl64(old[0] * 5, 7) * 9;
new[1] = old[0] ^ old[1];
new[0] = rotl64(old[0], 24) ^ new[1] ^ (new[1] << 16); // a, b
new[1] = rotl64(new[1], 37); // c
@ -5051,7 +5049,7 @@ uint64_t ha_random64()
HA_SPIN_UNLOCK(OTHER_LOCK, &rand_lock);
#endif
#endif
return result;
return rotl64(old[0] * 5, 7) * 9;
}
/* seeds the random state using up to <len> bytes from <seed>, starting with