24 lines
644 B
C
24 lines
644 B
C
#include "rand.h"
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static unsigned long long mcg_state = 0xcafef00dd15ea5e5u; // Must be odd
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static unsigned long long const multiplier = 6364136223846793005u;
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// https://en.wikipedia.org/wiki/Permuted_congruential_generator
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static unsigned long fast_rand(void) {
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unsigned long long x = mcg_state;
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unsigned count = (unsigned)(x >> 61);
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mcg_state = x * multiplier;
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x ^= x >> 22;
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return (unsigned long)(x >> (22 + count));
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}
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void rand_set_seed(unsigned long long seed) {
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mcg_state = 2 * seed + 1;
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(void)fast_rand();
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}
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unsigned int rand_uint(const unsigned int max) {
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return max == 0 ? 0 : (unsigned int)(fast_rand() % max);
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}
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