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Performance improvements in new PRNG

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This commit is contained in:
wiire-a 2017-12-02 01:19:18 +01:00
parent 3cd589c641
commit dfdc7c7717
2 changed files with 22 additions and 4 deletions
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13
src/random/glibc_random.c
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@ -52,8 +52,17 @@ static void glibc_seed(struct glibc_prng *prng, uint32_t seed)
uint32_t *state = prng->state;
prng->index = 344;
state[i++] = seed;
for ( ; i < 31; i++)
state[i] = (16807LL * state[i - 1]) % 0x7fffffff;
for ( ; i < 31; i++) {
/* This does: state[i] = (16807LL * state[i - 1]) % 0x7fffffff
using the sum of digits method which works for mod N, base N+1 */
const uint64_t p = 16807ULL * state[i - 1];
const uint64_t m = (p >> 31) + (p & 0x7fffffff);
/* The result might still not fit in 31 bits, if not, repeat
(conditional seems to make it slighlty faster) */
state[i] = (m & 0xffffffff80000000) ? ((m >> 31) + (m & 0x7fffffff)) : m;
}
for (i = 31; i < 34; i++) state[i] = state[i - 31];
for (i = 34; i < 344; i++) state[i] = state[i - 31] + state[i - 3];
}

13
src/random/glibc_random_lazy.c
View File

@ -51,8 +51,17 @@ static void glibc_lazyseed(struct glibc_lazyprng *prng, uint32_t seed)
uint32_t *state = prng->state;
uint32_t i = 0;
state[i++] = seed;
for ( ; i < 31; i++)
state[i] = (16807LL * state[i - 1]) % 0x7fffffff;
for ( ; i < 31; i++) {
/* This does: state[i] = (16807LL * state[i - 1]) % 0x7fffffff
using the sum of digits method which works for mod N, base N+1 */
const uint64_t p = 16807ULL * state[i - 1];
const uint64_t m = (p >> 31) + (p & 0x7fffffff);
/* The result might still not fit in 31 bits, if not, repeat
(conditional seems to make it slighlty faster) */
state[i] = (m & 0xffffffff80000000) ? ((m >> 31) + (m & 0x7fffffff)) : m;
}
for (i = 31; i < 34; i++) state[i] = state[i - 31];
for (i = 34; i < 344 - 3 + 1; i++) state[i] = state[i - 31] + state[i - 3];
}