added random number generation algorithms

src/random/xoroshiro/32bitValue/xoroshiro64star.c

@@ -0,0 +1,53 @@
+/*  Written in 2016 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 "../../krandom.h"
+
+/*  
+This is xoroshiro64* 1.0, our best and fastest 32-bit small-state
+generator for 32-bit floating-point numbers. We suggest to use its
+upper bits for floating-point generation, as it is slightly faster than
+xoroshiro64**. It passes all tests we are aware of except for linearity
+tests, as the lowest six bits have low linear complexity, so if low
+linear complexity is not considered an issue (as it is usually the
+case) it can be used to generate 32-bit outputs, too.
+
+We suggest to use a sign test to extract a random Boolean value, and
+right shifts to extract subsets of bits.
+
+The state must be seeded so that it is not everywhere zero. 
+*/
+
+static inline uint32 rotl(const uint32 x, int k) {
+    return (x << k) | (x >> (32 - k));
+}
+
+typedef union {
+    uint64 merged;
+    uint32 s[2];
+} _state_t;
+
+uint32 xoroshiro64star_next(void* _state) {
+    _state_t* state=_state;
+    const uint32 s0 = state->s[0];
+    uint32 s1 = state->s[1];
+    const uint32 result = s0 * 0x9E3779BB;
+
+    s1 ^= s0;
+    state->s[0] = rotl(s0, 26) ^ s1 ^ (s1 << 9); // a, b
+    state->s[1] = rotl(s1, 13); // c
+
+    return result;
+}
+
+void* xoroshiro64star_init(uint64 seed){
+    _state_t* state=malloc(sizeof(_state_t));
+    splitmix64_state splitmix=splitmix64_init(seed);
+    state->merged=splitmix64_next(splitmix);
+    return state;
+}