MINOR: tools/rnd: compute the result outside of the CAS loop
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.
diff --git a/src/tools.c b/src/tools.c
index de5dfa8..718bb49 100644
--- a/src/tools.c
+++ b/src/tools.c
@@ -5021,7 +5021,6 @@
*/
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 @@
#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 @@
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