35 lines
1.2 KiB
C
35 lines
1.2 KiB
C
#include "splitmix64.h"
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/*
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This is a fixed-increment version of Java 8's SplittableRandom generator
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See http://dx.doi.org/10.1145/2714064.2660195 and
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http://docs.oracle.com/javase/8/docs/api/java/util/SplittableRandom.html
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It is a very fast generator passing BigCrush, and it can be useful if
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for some reason you absolutely want 64 bits of state; otherwise, we
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rather suggest to use a xoroshiro128+ (for moderately parallel
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computations) or xorshift1024* (for massively parallel computations)
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generator.
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*/
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// The state can be seeded with any (upto) 64 bit integer value.
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void* splitmix64_init(u64 seed){
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splitmix64_state* state=malloc(sizeof(splitmix64_state));
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*state=seed;
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return state;
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}
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u64 splitmix64_next(void* _state) {
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splitmix64_state* state=_state;
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// increment the state variable
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*state += 0x9e3779b97f4a7c15;
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// copy the state to a working variable
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u64 z = *state;
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// xor the variable with the variable right bit shifted 30 then multiply by a constant
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z = (z ^ (z>>30)) * 0xbf58476d1ce4e5b9;
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// xor the variable with the variable right bit shifted 27 then multiply by a constant
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z = (z ^ (z>>27)) * 0x94d049bb133111eb;
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// return the variable xored with itself right bit shifted 31
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return z ^ (z>>31);
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}
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