mirror of
https://github.com/TerryCavanagh/VVVVVV.git
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e6a3df6ca6
In its previous location, it would only print the value of `s` after it had been mutated by `splitmix32` four times, and it doesn't get used after that, so the print isn't very useful. Mixing code and declarations here is fine because starting from a few months ago, we compile with C99 and if we ever need to compile with C90 then it's trivial to add braces surrounding the declarations.
69 lines
1.2 KiB
C
69 lines
1.2 KiB
C
#include <stdint.h>
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#include "Vlogging.h"
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/* Implements the xoshiro128+ PRNG. */
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static uint32_t rotl(const uint32_t x, const int k)
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{
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return (x << k) | (x >> (32 - k));
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}
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static uint32_t s[4];
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static uint32_t splitmix32(uint32_t* x)
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{
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uint32_t z = (*x += 0x9e3779b9UL);
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z = (z ^ (z >> 15)) * 0xbf58476dUL;
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z = (z ^ (z >> 13)) * 0x94d049bbUL;
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return z ^ (z >> 16);
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}
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static void seed(
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const uint32_t s0,
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const uint32_t s1,
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const uint32_t s2,
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const uint32_t s3
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) {
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s[0] = s0;
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s[1] = s1;
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s[2] = s2;
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s[3] = s3;
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}
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uint32_t xoshiro_next(void)
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{
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const uint32_t result = s[0] + s[3];
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const uint32_t t = s[1] << 9;
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s[2] ^= s[0];
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s[3] ^= s[1];
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s[1] ^= s[2];
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s[0] ^= s[3];
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s[2] ^= t;
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s[3] = rotl(s[3], 11);
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vlog_debug("Next xoshiro is %u.", result);
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return result;
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}
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void xoshiro_seed(uint32_t s)
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{
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vlog_debug("Xoshiro seeded with %u.", s);
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const uint32_t s0 = splitmix32(&s);
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const uint32_t s1 = splitmix32(&s);
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const uint32_t s2 = splitmix32(&s);
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const uint32_t s3 = splitmix32(&s);
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seed(s0, s1, s2, s3);
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}
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float xoshiro_rand(void)
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{
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return ((float) xoshiro_next()) / ((float) UINT32_MAX);
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}
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