90 lines
2.7 KiB
C++
90 lines
2.7 KiB
C++
/*
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* Copyright (C) 2020, Evan Sultanik
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* Public Domain
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*
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* An implementation of the MT19937 Algorithm for the Mersenne Twister
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* by Evan Sultanik. Based upon the pseudocode in: M. Matsumoto and
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* T. Nishimura, "Mersenne Twister: A 623-dimensionally
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* equidistributed uniform pseudorandom number generator," ACM
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* Transactions on Modeling and Computer Simulation Vol. 8, No. 1,
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* January pp.3-30 1998.
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*
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* http://www.sultanik.com/Mersenne_twister
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*/
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#include <Source/RuntimeInternal.hpp>
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#include "mtwister.hpp"
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#define UPPER_MASK 0x80000000
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#define LOWER_MASK 0x7fffffff
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#define TEMPERING_MASK_B 0x9d2c5680
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#define TEMPERING_MASK_C 0xefc60000
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inline static void MT_SeedRand(MTRand *rand, AuUInt32 seed)
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{
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/* set initial seeds to mt[STATE_VECTOR_LENGTH] using the generator
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* from Line 25 of Table 1 in: Donald Knuth, "The Art of Computer
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* Programming," Vol. 2 (2nd Ed.) pp.102.
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*/
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rand->mt[0] = seed & 0xffffffff;
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for (rand->index = 1; rand->index < STATE_VECTOR_LENGTH; rand->index++)
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{
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rand->mt[rand->index] = (6069 * rand->mt[rand->index - 1]) & 0xffffffff;
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}
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}
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/**
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* Creates a new random number generator from a given seed.
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*/
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MTRand MT_SeedRand(AuUInt32 seed)
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{
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MTRand rand {};
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MT_SeedRand(&rand, seed);
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return rand;
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}
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/**
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* Generates a pseudo-randomly generated long.
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*/
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AuUInt32 MT_NextLong(MTRand *rand)
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{
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AuUInt32 y;
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static const AuUInt32 mag[2] = {0x0, 0x9908b0df}; /* mag[x] = x * 0x9908b0df for x = 0,1 */
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rand->lock.Lock();
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if (rand->index >= STATE_VECTOR_LENGTH || rand->index < 0)
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{
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int kk;
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/* generate STATE_VECTOR_LENGTH words at a time */
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if (rand->index >= STATE_VECTOR_LENGTH + 1 || rand->index < 0)
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{
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MT_SeedRand(rand, 4357);
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}
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for (kk = 0; kk < STATE_VECTOR_LENGTH - STATE_VECTOR_M; kk++)
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{
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y = (rand->mt[kk] & UPPER_MASK) | (rand->mt[kk + 1] & LOWER_MASK);
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rand->mt[kk] = rand->mt[kk + STATE_VECTOR_M] ^ (y >> 1) ^ mag[y & 0x1];
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}
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for (; kk < STATE_VECTOR_LENGTH - 1; kk++)
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{
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y = (rand->mt[kk] & UPPER_MASK) | (rand->mt[kk + 1] & LOWER_MASK);
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rand->mt[kk] = rand->mt[kk + (STATE_VECTOR_M - STATE_VECTOR_LENGTH)] ^ (y >> 1) ^ mag[y & 0x1];
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}
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y = (rand->mt[STATE_VECTOR_LENGTH - 1] & UPPER_MASK) | (rand->mt[0] & LOWER_MASK);
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rand->mt[STATE_VECTOR_LENGTH - 1] = rand->mt[STATE_VECTOR_M - 1] ^ (y >> 1) ^ mag[y & 0x1];
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rand->index = 0;
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}
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y = rand->mt[rand->index++];
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y ^= (y >> 11);
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y ^= (y << 7) & TEMPERING_MASK_B;
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y ^= (y << 15) & TEMPERING_MASK_C;
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y ^= (y >> 18);
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rand->lock.Unlock();
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return y;
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} |