kitchen: README + MISSIONS/engine-c keep-drop notes

engine-c/src/rng.c

@@ -0,0 +1,42 @@
+#include "kknd.h"
+
+/* xoroshiro128** deterministic RNG */
+
+void rng_seed(RNG *r, uint64_t seed) {
+    if (seed == 0) seed = 0x9E3779B97F4A7C15ULL;
+    r->s[0] = seed;
+    r->s[1] = seed ^ 0xBF58476D1CE4E5B9ULL;
+    if (r->s[0] == 0) r->s[0] = 1;
+    if (r->s[1] == 0) r->s[1] = 2;
+}
+
+static inline uint64_t rotl(uint64_t x, int k) {
+    return (x << k) | (x >> (64 - k));
+}
+
+uint64_t rng_u64(RNG *r) {
+    uint64_t s0 = r->s[0];
+    uint64_t s1 = r->s[1];
+    uint64_t result = rotl(s0 * 5, 7) * 9;
+    s1 ^= s0;
+    r->s[0] = rotl(s0, 24) ^ s1 ^ (s1 << 16);
+    r->s[1] = rotl(s1, 37);
+    return result;
+}
+
+uint32_t rng_u32(RNG *r) {
+    return (uint32_t)(rng_u64(r) >> 32);
+}
+
+int rng_range(RNG *r, int lo, int hi) {
+    if (hi <= lo) return lo;
+    return lo + (int)(rng_u32(r) % (uint32_t)(hi - lo + 1));
+}
+
+float rng_f32(RNG *r) {
+    return (float)(rng_u32(r) >> 8) / (float)(1 << 24);
+}
+
+float rng_frange(RNG *r, float lo, float hi) {
+    return lo + rng_f32(r) * (hi - lo);
+}