62 lines
1.6 KiB
C++
62 lines
1.6 KiB
C++
#define MODULE "rand"
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#include "rand/Mersenne.h"
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#include "assert.h"
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#include <stddef.h>
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typedef uint64_t word_t;
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static const int STATE_SIZE = 312;
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static const int MIDDLE = 156;
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static const int INIT_SHIFT = 62;
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static const uint64_t TWIST_MASK = 0xb5026f5aa96619e9;
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static const uint64_t INIT_FACT = 6364136223846793005;
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static const int SHIFT1 = 29;
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static const uint64_t MASK1 = 0x5555555555555555;
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static const int SHIFT2 = 17;
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static const uint64_t MASK2 = 0x71d67fffeda60000;
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static const int SHIFT3 = 37;
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static const uint64_t MASK3 = 0xfff7eee000000000;
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static const int SHIFT4 = 43;
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static const word_t LOWER_MASK = 0x7fffffff;
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static const word_t UPPER_MASK = (~(word_t)LOWER_MASK);
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static word_t state[STATE_SIZE];
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static size_t index = STATE_SIZE + 1;
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void Mersenne::seed(uint64_t s)
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{
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index = STATE_SIZE;
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state[0] = s;
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for (size_t i = 1; i < STATE_SIZE; i++) state[i] = (INIT_FACT * (state[i - 1] ^ (state[i - 1] >> INIT_SHIFT))) + i;
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}
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static void twist()
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{
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for (size_t i = 0; i < STATE_SIZE; i++)
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{
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word_t x = (state[i] & UPPER_MASK) | (state[(i + 1) % STATE_SIZE] & LOWER_MASK);
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x = (x >> 1) ^ (x & 1 ? TWIST_MASK : 0);
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state[i] = state[(i + MIDDLE) % STATE_SIZE] ^ x;
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}
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index = 0;
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}
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uint64_t Mersenne::get()
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{
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if (index >= STATE_SIZE)
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{
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ASSERT(index == STATE_SIZE && "Mersenne generator was never seeded");
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twist();
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}
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word_t y = state[index];
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y ^= (y >> SHIFT1) & MASK1;
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y ^= (y << SHIFT2) & MASK2;
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y ^= (y << SHIFT3) & MASK3;
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y ^= y >> SHIFT4;
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index++;
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return y;
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} |