65 lines
1.4 KiB
C
65 lines
1.4 KiB
C
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/*
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* This rand() implementation is based on the Mersenne Twister.
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* Specifically, it's a C implementation of the pseudocode
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* implementation that can be found on the Wikipedia article for
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* the Mersenne Twister.
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*
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* Did we have to do a Mersenne Twister? No. No, we did not.
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* Did we? Fuck yes, we did.
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*
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* Love,
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* Kat
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*/
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#include <stdlib.h>
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static int _rand_state[624] = { 0 };
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static unsigned int _rand_seed = 5489;
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static int _rand_index = 625;
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void _rand_init(unsigned int seed) {
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_rand_index = 624;
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_rand_state[0] = seed;
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int i = 0;
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for(i = 1; i < 624; i++) {
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_rand_state[i] = 1812433253 ;
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_rand_state[i] *= _rand_state[i-1] ^ (_rand_state[i-1] >> 30);
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_rand_state[i] += i;
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}
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}
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void _rand_twist() {
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int i = 0, x, xA;
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for(i = 0; i < 624; i++) {
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x = _rand_state[i] & 0xFFFF0000 + (_rand_state[(i + 1) % 624] & 0xFFFF);
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xA = x % 2 == 0 ? x >> 1 : (x >> 1) ^ 0x9908B0DF;
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_rand_state[i] = _rand_state[(i + 397) % 624] ^ xA;
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}
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_rand_index = 0;
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}
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int rand(void) {
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int y;
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if(_rand_index > 624) {
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_rand_init(_rand_seed);
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}
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if(_rand_index >= 624) {
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_rand_twist();
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}
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y = _rand_state[_rand_index];
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y ^= y >> 11;
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y ^= (y << 7) & 0x9D2C5680;
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y ^= (y << 15) & 0xEFC60000;
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y ^= (y >> 18);
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_rand_index++;
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return y % RAND_MAX;
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}
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void srand(unsigned int seed) {
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_rand_seed = seed;
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_rand_index = 625;
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}
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