diff options
Diffstat (limited to 'random.c')
-rw-r--r-- | random.c | 63 |
1 files changed, 63 insertions, 0 deletions
diff --git a/random.c b/random.c new file mode 100644 index 0000000..f0a06c2 --- /dev/null +++ b/random.c @@ -0,0 +1,63 @@ +/* Psoudo-random number generator + * + * Uses xorshift1024 from “An experimental exploration of Marsaglia’s xorshift + * generators, scrambled”, Sebastiano Vigna + */ + +#include "random.h" + +uint64_t rand_u64 (randctx * const st) { + uint64_t s0 = st->s[ st->p ]; + uint64_t s1 = st->s[ st->p = ( st->p + 1 ) & (XORSHIFT_S-1) ]; + s1 ^= s1 << 31; // a + s1 ^= s1 >> 11; // b + s0 ^= s0 >> 30; // c + return ( st->s[ st->p ] = s0 ^ s1 ) * 1181783497276652981LL; +} + +/* Generate random double in [0,1] + */ +double rand_d01 (randctx * const st) { + return (double) rand_u64 (st) / (double) UINT64_MAX; +} + +/* Generate random double in [-1,1] + */ +double rand_d11 (randctx * const st) { + return rand_d01 (st) * 2.0 - 1.0; +} + +/* Random boolean value in {0,1} + */ +int rand_bool (randctx * const st) { + return rand_u64 (st) & 1; +} + +/* Generate random uint64_t with Intel’s rdrand instruction + */ +static uint64_t rand64 () { + unsigned long long rand; + while (!__builtin_ia32_rdrand64_step (&rand)); + return rand; +} + +/* Seed rng with rdrand + */ +void rand_seed (randctx * const st) { + /* seed with high-quality randomness */ + for (unsigned char i = 0; i < XORSHIFT_S; i++) { + st->s[i] = rand64 (); + } +} + +#if 0 +uint64_t xorshift_step (randctx * const st) { + uint64_t x = st->s[0]; + x ^= x >> 12; // a + x ^= x << 25; // b + x ^= x >> 27; // c + st->s[0] = x; + return x * 2685821657736338717LL; +} +#endif + |