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ITS#9599 Switch to xorshift for random numbers

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This commit is contained in:
Ondřej Kuzník 2021-09-23 14:29:45 +01:00 committed by Quanah Gibson-Mount
parent 3c07544b2a
commit 8968d13163
1 changed files with 21 additions and 13 deletions
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34
servers/lloadd/tier_bestof.c
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@ -30,26 +30,29 @@ static LloadTierSelect bestof_select;
struct lload_tier_type bestof_tier;
/*
* Linear Congruential Generator - we don't need
* high quality randomness, and we don't want to
* interfere with anyone else's use of srand().
* xorshift - we don't need high quality randomness, and we don't want to
* interfere with anyone else's use of srand() but we still want something with
* little bias.
*
* The PRNG here cycles thru 941,955 numbers.
* The PRNG here cycles thru 2^64−1 numbers.
*/
static float bestof_seed;
static uint64_t bestof_seed;
static void
bestof_srand( int seed )
{
bestof_seed = (float)seed / (float)RAND_MAX;
bestof_seed = seed;
}
static float
static uint64_t
bestof_rand()
{
float val = 9821.0 * bestof_seed + .211327;
bestof_seed = val - (int)val;
return bestof_seed;
uint64_t val = bestof_seed;
val ^= val << 13;
val ^= val >> 7;
val ^= val << 17;
bestof_seed = val;
return val;
}
static int
@ -84,6 +87,7 @@ LloadTier *
bestof_init( void )
{
LloadTier *tier;
int seed;
tier = ch_calloc( 1, sizeof(LloadTier) );
@ -91,7 +95,11 @@ bestof_init( void )
ldap_pvt_thread_mutex_init( &tier->t_mutex );
LDAP_CIRCLEQ_INIT( &tier->t_backends );
bestof_srand( rand() );
/* Make sure we don't pass 0 as a seed */
do {
seed = rand();
} while ( !seed );
bestof_srand( seed );
return tier;
}
@ -227,8 +235,8 @@ bestof_select(
}
/* Pick two backend indices at random */
i0 = bestof_rand() * n;
i1 = bestof_rand() * ( n - 1 );
i0 = bestof_rand() % n;
i1 = bestof_rand() % ( n - 1 );
if ( i1 >= i0 ) {
i1 += 1;
} else {