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/* Copyright (C) 2011 Wildfire Games.
* This file is part of 0 A.D.
*
* 0 A.D. is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 2 of the License, or
* (at your option) any later version.
*
* 0 A.D. is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with 0 A.D. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef INCLUDED_MATHS_RANDOM
#define INCLUDED_MATHS_RANDOM
/**
* Random number generator with period 2^{512}-1;
* effectively a better version of MT19937 (smaller state, similarly fast,
* simpler code, better distribution).
* Implements Boost.Random's PseudoRandomNumberGenerator concept.
*/
class WELL512
{
private:
uint32_t state[16];
uint32_t index;
public:
WELL512()
{
seed((uint32_t)0);
}
uint32_t operator()()
{
// WELL512 implementation by Chris Lomont (Game Programming Gems 7;
// http://lomont.org/Math/Papers/2008/Lomont_PRNG_2008.pdf)
uint32_t a, b, c, d;
a = state[index];
c = state[(index + 13) & 15];
b = a ^ c ^ (a << 16) ^ (c << 15);
c = state[(index + 9) & 15];
c ^= (c >> 11);
a = state[index] = b ^ c;
d = a ^ ((a << 5) & 0xDA442D24UL);
index = (index + 15) & 15;
a = state[index];
state[index] = a ^ b ^ d ^ (a << 2) ^ (b << 18) ^ (c << 28);
return state[index];
}
void seed(uint32_t value)
{
index = 0;
// Expand the seed with the same algorithm as boost::random::mersenne_twister
const uint32_t mask = ~0u;
state[0] = value & mask;
for (uint32_t i = 1; i < ARRAY_SIZE(state); ++i)
state[i] = (1812433253UL * (state[i - 1] ^ (state[i - 1] >> 30)) + i) & mask;
}
void seed(uint32_t values[16])
{
index = 0;
for (uint32_t i = 0; i < ARRAY_SIZE(state); ++i)
state[i] = values[i];
}
// Implement UniformRandomNumberGenerator concept:
typedef uint32_t result_type;
uint32_t min() const
{
return std::numeric_limits<uint32_t>::min();
}
uint32_t max() const
{
return std::numeric_limits<uint32_t>::max();
}
// Implement EqualityComparable concept:
friend bool operator==(const WELL512& x, const WELL512& y)
{
if (x.index != y.index)
return false;
for (uint32_t i = 0; i < ARRAY_SIZE(x.state); ++i)
if (x.state[i] != y.state[i])
return false;
return true;
}
friend bool operator!=(const WELL512& x, const WELL512& y)
{
return !(x == y);
}
// Implement Streamable concept (based on boost::random::mersenne_twister):
template<class CharT, class Traits>
friend std::basic_ostream<CharT, Traits>&
operator<<(std::basic_ostream<CharT, Traits>& os, const WELL512& rng)
{
os << rng.index << " ";
for (uint32_t i = 0; i < ARRAY_SIZE(rng.state); ++i)
os << rng.state[i] << " ";
return os;
}
template<class CharT, class Traits>
friend std::basic_istream<CharT, Traits>&
operator>>(std::basic_istream<CharT, Traits>& is, WELL512& rng)
{
is >> rng.index >> std::ws;
for (uint32_t i = 0; i < ARRAY_SIZE(rng.state); ++i)
is >> rng.state[i] >> std::ws;
return is;
}
};
#endif // INCLUDED_MATHS_RANDOM
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