Added a version of xoroshiro128+

Author: lh3

krng.h

@@ -0,0 +1,54 @@
+#ifndef KRNG_H
+#define KRNG_H
+
+typedef struct {
+	uint64_t s[2];
+} krng_t;
+
+static inline uint64_t kr_splitmix64(uint64_t x)
+{
+	uint64_t z = (x += 0x9E3779B97F4A7C15ULL);
+	z = (z ^ (z >> 30)) * 0xBF58476D1CE4E5B9ULL;
+	z = (z ^ (z >> 27)) * 0x94D049BB133111EBULL;
+	return z ^ (z >> 31);
+}
+
+static inline uint64_t kr_rand_r(krng_t *r)
+{
+	const uint64_t s0 = r->s[0];
+	uint64_t s1 = r->s[1];
+	const uint64_t result = s0 + s1;
+	s1 ^= s0;
+	r->s[0] = (s0 << 55 | s0 >> 9) ^ s1 ^ (s1 << 14);
+	r->s[1] = s0 << 36 | s0 >> 28;
+	return result;
+}
+
+static inline void kr_jump_r(krng_t *r)
+{
+	static const uint64_t JUMP[] = { 0xbeac0467eba5facbULL, 0xd86b048b86aa9922ULL };
+	uint64_t s0 = 0, s1 = 0;
+	int i, b;
+	for (i = 0; i < 2; ++i)
+		for (b = 0; b < 64; b++) {
+			if (JUMP[i] & 1ULL << b)
+				s0 ^= r->s[0], s1 ^= r->s[1];
+			kr_rand_r(r);
+		}
+	r->s[0] = s0, r->s[1] = s1;
+}
+
+static inline void kr_srand_r(krng_t *r, uint64_t seed)
+{
+	r->s[0] = kr_splitmix64(seed);
+	r->s[1] = kr_splitmix64(r->s[0]);
+}
+
+static inline double kr_drand_r(krng_t *r)
+{
+	union { uint64_t i; double d; } u;
+	u.i = 0x3FFULL << 52 | kr_rand_r(r) >> 12;
+	return u.d - 1.0;
+}
+
+#endif