82 lines
2.2 KiB
C++
82 lines
2.2 KiB
C++
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/*
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* Copyright (C) 2008, Chris Lomont
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* Public Domain
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*
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* http://lomont.org/papers/2008/Lomont_PRNG_2008.pdf
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*/
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#include <RuntimeInternal.hpp>
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#include "WELL.hpp"
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#include "mtwister.hpp"
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// Redunced seed entropy should not matter to the extent that MT can make up for it.
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// WELL is used in the fast rng backend, and i feel as though it would be unreasonable
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// to go above UInt64 seeds. For toy purposes, U32 seeds are probably fine. Treat WELL
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// like MT without 624 prediction and performance issues.
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// Should we look into xorshift soon?
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// NOTE: Just to make it clear, the point is that MT entropy should be good enough
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// to maintain WELL and xorshift randomness, while acknowledging that reduced seed
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// entropy does make it easier to bruteforce especially if the index count is known.
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inline static void WELL_SeedRand(WELLRand *rand, AuUInt32 seed)
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{
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MTRand mtrand = MT_SeedRand(seed);
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for (unsigned int i = 0; i < 16; i++)
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{
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rand->state[i] = MT_NextLong(&mtrand);
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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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WELLRand WELL_SeedRand(AuUInt32 seed)
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{
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WELLRand rand {};
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WELL_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 WELL_NextLong(WELLRand *rand)
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{
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AuUInt32 a, b, c, d, ret;
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rand->lock.Lock();
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a = rand->state[rand->index];
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c = rand->state[(rand->index + 13) & 15];
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b = a ^ c ^ (a << 16) ^ (c << 15);
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c = rand->state[(rand->index + 9) & 15];
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c ^= (c >> 11);
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a = rand->state[rand->index] = b ^ c;
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d = a ^ ((a << 5) & 0xDA442D24UL);
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rand->index = (rand->index + 15) & 15;
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a = rand->state[rand->index];
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rand->state[rand->index] = a ^ b ^ d ^ (a << 2) ^ (b << 18) ^ (c << 28);
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ret = rand->state[rand->index];
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rand->lock.Unlock();
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return ret;
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}
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void WELL_NextBytes(WELLRand *rand, void *in, AuUInt32 length)
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{
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AuUInt i;
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AuUInt8 *base;
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i = 0;
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base = reinterpret_cast<AuUInt8 *>(in);
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for (; i < length; i += 4)
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{
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AuUInt32 rng = WELL_NextLong(rand);
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std::memcpy(base + i, &rng, 4);
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}
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if (i > length)
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{
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i -= 4;
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AuUInt32 padRng = WELL_NextLong(rand);
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std::memcpy(base + i, &padRng, length - i);
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}
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}
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