92 lines
1.3 KiB
C
92 lines
1.3 KiB
C
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#include "prng.h"
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// Define MT19937 constants (32-bit RNG)
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enum
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{
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// Assumes W = 32 (omitting this)
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N = 624,
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M = 397,
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R = 31,
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A = 0x9908B0DF,
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F = 1812433253,
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U = 11,
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// Assumes D = 0xFFFFFFFF (omitting this)
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S = 7,
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B = 0x9D2C5680,
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T = 15,
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C = 0xEFC60000,
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L = 18,
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MASK_LOWER = (1ull << R) - 1,
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MASK_UPPER = (1ull << R)
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};
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static uint32_t mt[N];
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static uint16_t index;
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// Re-init with a given seed
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void InitializePRNG(const uint32_t seed)
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{
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uint32_t i;
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mt[0] = seed;
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for ( i = 1; i < N; i++ )
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{
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mt[i] = (F * (mt[i - 1] ^ (mt[i - 1] >> 30)) + i);
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}
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index = N;
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}
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static void Twist(void)
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{
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uint32_t i, x, xA;
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for ( i = 0; i < N; i++ )
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{
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x = (mt[i] & MASK_UPPER) + (mt[(i + 1) % N] & MASK_LOWER);
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xA = x >> 1;
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if ( x & 0x1 )
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xA ^= A;
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mt[i] = mt[(i + M) % N] ^ xA;
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}
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index = 0;
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}
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// Obtain a 32-bit random number
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uint32_t ExtractU32(void)
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{
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uint32_t y;
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int i = index;
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if ( index >= N )
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{
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Twist();
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i = index;
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}
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y = mt[i];
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index = i + 1;
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y ^= (mt[i] >> U);
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y ^= (y << S) & B;
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y ^= (y << T) & C;
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y ^= (y >> L);
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return y;
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}
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int getrandom(int low, int high) {
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return ((ExtractU32() % high) + low);
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}
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