diff --git a/xorshift.c b/xorshift.c new file mode 100644 index 0000000..5dbec96 --- /dev/null +++ b/xorshift.c @@ -0,0 +1,60 @@ +#include +#include +#include + +struct xorshift32_state { + uint32_t a; +}; + +/* The state must be initialized to non-zero */ +uint32_t xorshift32(struct xorshift32_state *state) { + /* Algorithm "xor" from p. 4 of Marsaglia, "Xorshift RNGs" */ + uint32_t x = state->a; + x ^= x << 13; + x ^= x >> 17; + x ^= x << 5; + return state->a = x; +} + +struct xorshift64_state { + uint64_t a; +}; + +/* The state must be initialized to non-zero */ +uint64_t xorshift64(struct xorshift64_state *state) { + uint64_t x = state->a; + x ^= x << 13; + x ^= x >> 7; + x ^= x << 17; + return state->a = x; +} + +/* struct xorshift128_state can alternatively be defined as a pair + of uint64_t or a uint128_t where supported */ +struct xorshift128_state { + uint32_t x[4]; +}; + +/* The state must be initialized to non-zero */ +uint32_t xorshift128(struct xorshift128_state *state) { + /* Algorithm "xor128" from p. 5 of Marsaglia, "Xorshift RNGs" */ + uint32_t t = state->x[3]; + + uint32_t s = state->x[0]; /* Perform a contrived 32-bit shift. */ + state->x[3] = state->x[2]; + state->x[2] = state->x[1]; + state->x[1] = s; + + t ^= t << 11; + t ^= t >> 8; + return state->x[0] = t ^ s ^ (s >> 19); +} + +int main(void) { + struct xorshift32_state s = {}; + s.a = time(0); + + for (int a = 0; a < 10; a++) { + printf("Number %d: %d\n", a, xorshift32(&s)); + } +}