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* Please obtain a copy of the License at
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#include "random.h"
#include <machine/machine_routines.h>
// written in 2015 by Sebastiano Vigna https://prng.di.unimi.it/splitmix64.c
static inline uint64_t
splitmix64_next(uint64_t *state)
{
uint64_t z = (*state += 0x9e3779b97f4a7c15);
z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9;
z = (z ^ (z >> 27)) * 0x94d049bb133111eb;
return z ^ (z >> 31);
}
static inline uint64_t
rotl64(uint64_t x, int8_t r)
{
return (x << r) | (x >> (64 - r));
}
// fast alternative to x % n
static inline uint64_t
fast_bound(uint64_t x, uint64_t n)
{
uint128_t mul = (uint128_t)x * (uint128_t)n;
return (uint64_t)(mul >> 64);
}
// initial state as if random_set_seed(1337) was called
uint64_t romuduojr_x_state = 13161956497586561035ull;
uint64_t romuduojr_y_state = 14663483216071361993ull;
void
random_set_seed(uint64_t seed)
{
romuduojr_x_state = splitmix64_next(&seed);
romuduojr_y_state = splitmix64_next(&seed);
}
uint64_t
random_next(void)
{
const uint64_t xp = romuduojr_x_state;
romuduojr_x_state = 15241094284759029579ull * romuduojr_y_state;
romuduojr_y_state = romuduojr_y_state - xp;
romuduojr_y_state = rotl64(romuduojr_y_state, 27);
return xp;
}
uint64_t
random_below(uint64_t upper_bound)
{
return fast_bound(random_next(), upper_bound);
}