random routines

test_scripts/pseudorandom_gens/xoroshiro64starstar.c

@@ -0,0 +1,50 @@
+// https://prng.di.unimi.it/xoroshiro64starstar.c
+
+/*  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.
+
+Permission to use, copy, modify, and/or distribute this software for any
+purpose with or without fee is hereby granted.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR
+IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
+
+#include <stdint.h>
+
+/* This is xoroshiro64** 1.0, our 32-bit all-purpose, rock-solid,
+   small-state generator. It is extremely fast and it passes all tests we
+   are aware of, but its state space is not large enough for any parallel
+   application.
+
+   For generating just single-precision (i.e., 32-bit) floating-point
+   numbers, xoroshiro64* is even faster.
+
+   The state must be seeded so that it is not everywhere zero. */
+
+
+static inline uint32_t rotl(const uint32_t x, int k) {
+	return (x << k) | (x >> (32 - k));
+}
+
+
+static uint32_t s[2];
+
+uint32_t next(void) {
+	const uint32_t s0 = s[0];
+	uint32_t s1 = s[1];
+	const uint32_t result = rotl(s0 * 0x9E3779BB, 5) * 5;
+
+	s1 ^= s0;
+	s[0] = rotl(s0, 26) ^ s1 ^ (s1 << 9); // a, b
+	s[1] = rotl(s1, 13); // c
+
+	return result;
+}