Replace rand() by xoshiro256** with per-mesh state.

[meshlink] / src / xoshiro.c

diff --git a/src/xoshiro.c b/src/xoshiro.c
new file mode 100644 (file)
index 0000000..c05e940
--- /dev/null
+++ b/src/xoshiro.c
@@ -0,0 +1,42 @@
+/*  Written in 2018 by David Blackman and Sebastiano Vigna (vigna@acm.org)
+
+To the extent possible under law, the author has dedicated all copyright
+and related and neighboring rights to this software to the public domain
+worldwide. This software is distributed without any warranty.
+
+See <http://creativecommons.org/publicdomain/zero/1.0/>. */
+
+#include <stdint.h>
+#include "xoshiro.h"
+
+/* This is xoshiro256** 1.0, one of our all-purpose, rock-solid
+   generators. It has excellent (sub-ns) speed, a state (256 bits) that is
+   large enough for any parallel application, and it passes all tests we
+   are aware of.
+
+   For generating just floating-point numbers, xoshiro256+ is even faster.
+
+   The state must be seeded so that it is not everywhere zero. If you have
+   a 64-bit seed, we suggest to seed a splitmix64 generator and use its
+   output to fill s. */
+
+static inline uint64_t rotl(const uint64_t x, int k) {
+       return (x << k) | (x >> (64 - k));
+}
+
+uint64_t xoshiro(uint64_t s[4]) {
+       const uint64_t result = rotl(s[1] * 5, 7) * 9;
+
+       const uint64_t t = s[1] << 17;
+
+       s[2] ^= s[0];
+       s[3] ^= s[1];
+       s[1] ^= s[2];
+       s[0] ^= s[3];
+
+       s[2] ^= t;
+
+       s[3] = rotl(s[3], 45);
+
+       return result;
+}