Add xorshift prng

src/prng/xorshift/xorshift.c

@@ -0,0 +1,89 @@
+#include "xorshift.h"
+#include "../../common/aliases/aliases.h"
+#include <stdbool.h>
+#include <stdlib.h>
+#include <time.h>
+
+typedef struct split_mix_64_state SplitMix64State;
+struct split_mix_64_state {
+  u64 seed;
+};
+
+internal u64 rol64(u64 x, u64 bits);
+internal u64 split_mix_64(SplitMix64State *state);
+
+XOR256State wapp_init_xor_256_state(void) {
+  persistent bool seeded = false;
+  if (!seeded) {
+    seeded = true;
+
+    struct timespec ts = {0};
+    clock_gettime(CLOCK_MONOTONIC_RAW, &ts);
+
+    srand48(ts.tv_nsec);
+  }
+
+  SplitMix64State sm64 = {.seed = lrand48()};
+
+  return (XOR256State){
+      .x = split_mix_64(&sm64),
+      .y = split_mix_64(&sm64),
+      .z = split_mix_64(&sm64),
+      .w = split_mix_64(&sm64),
+  };
+}
+
+u64 wapp_xorshift_256_generate(XOR256State *state) {
+  u64 t = state->x ^ (state->x << 11);
+
+  state->x = state->y;
+  state->y = state->z;
+  state->z = state->w;
+  state->w = (state->w ^ (state->w >> 19)) ^ (t ^ (t >> 8));
+
+  return state->w;
+}
+
+u64 wapp_xoshiro_256ss_generate(XOR256State *state) {
+  const u64 result = rol64(state->z * 5, 7) * 9;
+  const u64 t = state->z << 17;
+
+  state->y ^= state->w;
+  state->x ^= state->z;
+  state->z ^= state->y;
+  state->w ^= state->x;
+
+  state->y ^= t;
+  state->x = rol64(state->x, 45);
+
+  return result;
+}
+
+u64 wapp_xoshiro_256p_generate(XOR256State *state) {
+  const u64 result = state->w + state->x;
+  const u64 t = state->z << 17;
+
+  state->y ^= state->w;
+  state->x ^= state->z;
+  state->z ^= state->y;
+  state->w ^= state->x;
+
+  state->y ^= t;
+  state->x = rol64(state->x, 45);
+
+  return result;
+}
+
+internal u64 rol64(u64 x, u64 bits) {
+  return (x << bits) | (x >> (64 - bits));
+}
+
+internal u64 split_mix_64(SplitMix64State *state) {
+  state->seed += 0x9E3779B97f4A7C15;
+
+  u64 result = state->seed;
+  result = (result ^ (result >> 30)) * 0xBF58476D1CE4E5B9;
+  result = (result ^ (result >> 27)) * 0x94D049BB133111EB;
+
+  return result ^ (result >> 31);
+}