Unify prng use

Finally drop all isaac references, do not use system rng any more. Drop
rng state from flam3_frame – it was not used anyway.

1 files changed, 63 insertions, 0 deletions

diff --git a/random.c b/random.c
new file mode 100644
index 0000000..f0a06c2
--- /dev/null
+++ b/random.c
@@ -0,0 +1,63 @@
+/*	Psoudo-random number generator
+ *
+ *	Uses xorshift1024 from “An experimental exploration of Marsaglia’s xorshift
+ *	generators, scrambled”, Sebastiano Vigna
+ */
+
+#include "random.h"
+
+uint64_t rand_u64 (randctx * const st) {
+	uint64_t s0 = st->s[ st->p ];
+	uint64_t s1 = st->s[ st->p = ( st->p + 1 ) & (XORSHIFT_S-1) ];
+	s1 ^= s1 << 31; // a
+	s1 ^= s1 >> 11; // b
+	s0 ^= s0 >> 30; // c
+	return ( st->s[ st->p ] = s0 ^ s1 ) * 1181783497276652981LL;
+}
+
+/*	Generate random double in [0,1]
+ */
+double rand_d01 (randctx * const st) {
+	return (double) rand_u64 (st) / (double) UINT64_MAX;
+}
+
+/*	Generate random double in [-1,1]
+ */
+double rand_d11 (randctx * const st) {
+	return rand_d01 (st) * 2.0 - 1.0;
+}
+
+/*	Random boolean value in {0,1}
+ */
+int rand_bool (randctx * const st) {
+	return rand_u64 (st) & 1;
+}
+
+/*	Generate random uint64_t with Intel’s rdrand instruction
+ */
+static uint64_t rand64 () {
+	unsigned long long rand;
+	while (!__builtin_ia32_rdrand64_step (&rand));
+	return rand;
+}
+
+/*	Seed rng with rdrand
+ */
+void rand_seed (randctx * const st) {
+	/* seed with high-quality randomness */
+	for (unsigned char i = 0; i < XORSHIFT_S; i++) {
+		st->s[i] = rand64 ();
+	}
+}
+
+#if 0
+uint64_t xorshift_step (randctx * const st) {
+	uint64_t x = st->s[0];
+	x ^= x >> 12; // a
+	x ^= x << 25; // b
+	x ^= x >> 27; // c
+	st->s[0] = x;
+	return x * 2685821657736338717LL;
+}
+#endif
+