forked from personal/squiggle.c
28 lines
686 B
C
28 lines
686 B
C
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uint64_t xorshift64(uint64_t* seed)
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{
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// Algorithm "xor" from p. 4 of Marsaglia, "Xorshift RNGs"
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// <https://en.wikipedia.org/wiki/Xorshift>
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uint64_t x = *seed;
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x ^= x << 13;
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x ^= x >> 7;
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x ^= x << 17;
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return *seed = x;
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}
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double sample_unit_uniform(uint64_t* seed)
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{
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// samples uniform from [0,1] interval.
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return ((double)xorshift64(seed)) / ((double)UINT64_MAX);
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}
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double sample_unit_normal(uint64_t* seed)
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{
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// // See: <https://en.wikipedia.org/wiki/Box%E2%80%93Muller_transform>
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double u1 = sample_unit_uniform(seed);
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double u2 = sample_unit_uniform(seed);
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double z = sqrtf(-2.0 * log(u1)) * sin(2 * PI * u2);
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return z;
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}
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