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/* -*- C++ -*-
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*
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* This file is a part of LEMON, a generic C++ optimization library
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*
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* Copyright (C) 2003-2008
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* Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
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* (Egervary Research Group on Combinatorial Optimization, EGRES).
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*
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* Permission to use, modify and distribute this software is granted
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* provided that this copyright notice appears in all copies. For
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* precise terms see the accompanying LICENSE file.
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*
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* This software is provided "AS IS" with no warranty of any kind,
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* express or implied, and with no claim as to its suitability for any
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* purpose.
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*
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*/
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/*
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* This file contains the reimplemented version of the Mersenne Twister
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* Generator of Matsumoto and Nishimura.
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*
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* See the appropriate copyright notice below.
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*
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* Copyright (C) 1997 - 2002, Makoto Matsumoto and Takuji Nishimura,
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* 3. The names of its contributors may not be used to endorse or promote
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* products derived from this software without specific prior written
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* permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
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* OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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*
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* Any feedback is very welcome.
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* http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html
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* email: m-mat @ math.sci.hiroshima-u.ac.jp (remove space)
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*/
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#ifndef LEMON_RANDOM_H
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#define LEMON_RANDOM_H
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#include <algorithm>
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#include <iterator>
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#include <vector>
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#include <ctime>
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#include <cmath>
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#include <lemon/math.h>
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#include <lemon/dim2.h>
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///\ingroup misc
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///\file
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///\brief Mersenne Twister random number generator
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namespace lemon {
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namespace _random_bits {
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template <typename _Word, int _bits = std::numeric_limits<_Word>::digits>
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struct RandomTraits {};
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template <typename _Word>
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struct RandomTraits<_Word, 32> {
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typedef _Word Word;
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static const int bits = 32;
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static const int length = 624;
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static const int shift = 397;
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static const Word mul = 0x6c078965u;
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static const Word arrayInit = 0x012BD6AAu;
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static const Word arrayMul1 = 0x0019660Du;
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static const Word arrayMul2 = 0x5D588B65u;
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static const Word mask = 0x9908B0DFu;
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static const Word loMask = (1u << 31) - 1;
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static const Word hiMask = ~loMask;
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102 |
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103 |
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static Word tempering(Word rnd) {
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rnd ^= (rnd >> 11);
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rnd ^= (rnd << 7) & 0x9D2C5680u;
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rnd ^= (rnd << 15) & 0xEFC60000u;
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rnd ^= (rnd >> 18);
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return rnd;
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}
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};
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template <typename _Word>
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struct RandomTraits<_Word, 64> {
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typedef _Word Word;
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static const int bits = 64;
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static const int length = 312;
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static const int shift = 156;
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122 |
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123 |
static const Word mul = Word(0x5851F42Du) << 32 | Word(0x4C957F2Du);
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static const Word arrayInit = Word(0x00000000u) << 32 |Word(0x012BD6AAu);
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static const Word arrayMul1 = Word(0x369DEA0Fu) << 32 |Word(0x31A53F85u);
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static const Word arrayMul2 = Word(0x27BB2EE6u) << 32 |Word(0x87B0B0FDu);
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static const Word mask = Word(0xB5026F5Au) << 32 | Word(0xA96619E9u);
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static const Word loMask = (Word(1u) << 31) - 1;
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static const Word hiMask = ~loMask;
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static Word tempering(Word rnd) {
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rnd ^= (rnd >> 29) & (Word(0x55555555u) << 32 | Word(0x55555555u));
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rnd ^= (rnd << 17) & (Word(0x71D67FFFu) << 32 | Word(0xEDA60000u));
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rnd ^= (rnd << 37) & (Word(0xFFF7EEE0u) << 32 | Word(0x00000000u));
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rnd ^= (rnd >> 43);
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return rnd;
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}
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139 |
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140 |
};
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template <typename _Word>
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class RandomCore {
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public:
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145 |
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typedef _Word Word;
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147 |
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private:
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149 |
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static const int bits = RandomTraits<Word>::bits;
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static const int length = RandomTraits<Word>::length;
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static const int shift = RandomTraits<Word>::shift;
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154 |
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155 |
public:
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156 |
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157 |
void initState() {
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static const Word seedArray[4] = {
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0x12345u, 0x23456u, 0x34567u, 0x45678u
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160 |
};
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initState(seedArray, seedArray + 4);
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}
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164 |
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void initState(Word seed) {
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167 |
static const Word mul = RandomTraits<Word>::mul;
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current = state;
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170 |
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Word *curr = state + length - 1;
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curr[0] = seed; --curr;
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for (int i = 1; i < length; ++i) {
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curr[0] = (mul * ( curr[1] ^ (curr[1] >> (bits - 2)) ) + i);
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--curr;
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176 |
}
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177 |
}
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178 |
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179 |
template <typename Iterator>
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void initState(Iterator begin, Iterator end) {
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181 |
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182 |
static const Word init = RandomTraits<Word>::arrayInit;
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183 |
static const Word mul1 = RandomTraits<Word>::arrayMul1;
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184 |
static const Word mul2 = RandomTraits<Word>::arrayMul2;
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185 |
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186 |
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Word *curr = state + length - 1; --curr;
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Iterator it = begin; int cnt = 0;
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int num;
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190 |
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191 |
initState(init);
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192 |
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193 |
num = length > end - begin ? length : end - begin;
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while (num--) {
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curr[0] = (curr[0] ^ ((curr[1] ^ (curr[1] >> (bits - 2))) * mul1))
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+ *it + cnt;
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197 |
++it; ++cnt;
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198 |
if (it == end) {
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it = begin; cnt = 0;
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200 |
}
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if (curr == state) {
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curr = state + length - 1; curr[0] = state[0];
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203 |
}
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204 |
--curr;
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}
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206 |
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207 |
num = length - 1; cnt = length - (curr - state) - 1;
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208 |
while (num--) {
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curr[0] = (curr[0] ^ ((curr[1] ^ (curr[1] >> (bits - 2))) * mul2))
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- cnt;
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211 |
--curr; ++cnt;
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212 |
if (curr == state) {
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213 |
curr = state + length - 1; curr[0] = state[0]; --curr;
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214 |
cnt = 1;
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| 214 |
215 |
}
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216 |
}
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| 216 |
217 |
|
| 217 |
218 |
state[length - 1] = Word(1) << (bits - 1);
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| 218 |
219 |
}
|
| 219 |
220 |
|
| 220 |
221 |
void copyState(const RandomCore& other) {
|
| 221 |
222 |
std::copy(other.state, other.state + length, state);
|
| 222 |
223 |
current = state + (other.current - other.state);
|
| 223 |
224 |
}
|
| 224 |
225 |
|
| 225 |
226 |
Word operator()() {
|
| 226 |
227 |
if (current == state) fillState();
|
| 227 |
228 |
--current;
|
| 228 |
229 |
Word rnd = *current;
|
| 229 |
230 |
return RandomTraits<Word>::tempering(rnd);
|
| 230 |
231 |
}
|
| 231 |
232 |
|
| 232 |
233 |
private:
|
| 233 |
234 |
|
| 234 |
235 |
|
| 235 |
236 |
void fillState() {
|
| 236 |
237 |
static const Word mask[2] = { 0x0ul, RandomTraits<Word>::mask };
|
| 237 |
238 |
static const Word loMask = RandomTraits<Word>::loMask;
|
| 238 |
239 |
static const Word hiMask = RandomTraits<Word>::hiMask;
|
| 239 |
240 |
|
| 240 |
241 |
current = state + length;
|
| 241 |
242 |
|
| 242 |
243 |
register Word *curr = state + length - 1;
|
| 243 |
244 |
register long num;
|
| 244 |
245 |
|
| 245 |
246 |
num = length - shift;
|
| 246 |
247 |
while (num--) {
|
| 247 |
248 |
curr[0] = (((curr[0] & hiMask) | (curr[-1] & loMask)) >> 1) ^
|
| 248 |
249 |
curr[- shift] ^ mask[curr[-1] & 1ul];
|
| 249 |
250 |
--curr;
|
| 250 |
251 |
}
|
| 251 |
252 |
num = shift - 1;
|
| 252 |
253 |
while (num--) {
|
| 253 |
254 |
curr[0] = (((curr[0] & hiMask) | (curr[-1] & loMask)) >> 1) ^
|
| 254 |
255 |
curr[length - shift] ^ mask[curr[-1] & 1ul];
|
| 255 |
256 |
--curr;
|
| 256 |
257 |
}
|
| 257 |
258 |
state[0] = (((state[0] & hiMask) | (curr[length - 1] & loMask)) >> 1) ^
|
| 258 |
259 |
curr[length - shift] ^ mask[curr[length - 1] & 1ul];
|
| 259 |
260 |
|
| 260 |
261 |
}
|
| 261 |
262 |
|
| 262 |
263 |
|
| 263 |
264 |
Word *current;
|
| 264 |
265 |
Word state[length];
|
| ... |
... |
@@ -570,303 +571,303 @@
|
| 570 |
571 |
Random& operator=(const Random& other) {
|
| 571 |
572 |
if (&other != this) {
|
| 572 |
573 |
core.copyState(other.core);
|
| 573 |
574 |
}
|
| 574 |
575 |
return *this;
|
| 575 |
576 |
}
|
| 576 |
577 |
|
| 577 |
578 |
/// \brief Returns a random real number from the range [0, 1)
|
| 578 |
579 |
///
|
| 579 |
580 |
/// It returns a random real number from the range [0, 1). The
|
| 580 |
581 |
/// default Number type is \c double.
|
| 581 |
582 |
template <typename Number>
|
| 582 |
583 |
Number real() {
|
| 583 |
584 |
return _random_bits::RealConversion<Number, Word>::convert(core);
|
| 584 |
585 |
}
|
| 585 |
586 |
|
| 586 |
587 |
double real() {
|
| 587 |
588 |
return real<double>();
|
| 588 |
589 |
}
|
| 589 |
590 |
|
| 590 |
591 |
/// \brief Returns a random real number the range [0, b)
|
| 591 |
592 |
///
|
| 592 |
593 |
/// It returns a random real number from the range [0, b).
|
| 593 |
594 |
template <typename Number>
|
| 594 |
595 |
Number real(Number b) {
|
| 595 |
596 |
return real<Number>() * b;
|
| 596 |
597 |
}
|
| 597 |
598 |
|
| 598 |
599 |
/// \brief Returns a random real number from the range [a, b)
|
| 599 |
600 |
///
|
| 600 |
601 |
/// It returns a random real number from the range [a, b).
|
| 601 |
602 |
template <typename Number>
|
| 602 |
603 |
Number real(Number a, Number b) {
|
| 603 |
604 |
return real<Number>() * (b - a) + a;
|
| 604 |
605 |
}
|
| 605 |
606 |
|
| 606 |
607 |
/// \brief Returns a random real number from the range [0, 1)
|
| 607 |
608 |
///
|
| 608 |
609 |
/// It returns a random double from the range [0, 1).
|
| 609 |
610 |
double operator()() {
|
| 610 |
611 |
return real<double>();
|
| 611 |
612 |
}
|
| 612 |
613 |
|
| 613 |
614 |
/// \brief Returns a random real number from the range [0, b)
|
| 614 |
615 |
///
|
| 615 |
616 |
/// It returns a random real number from the range [0, b).
|
| 616 |
617 |
template <typename Number>
|
| 617 |
618 |
Number operator()(Number b) {
|
| 618 |
619 |
return real<Number>() * b;
|
| 619 |
620 |
}
|
| 620 |
621 |
|
| 621 |
622 |
/// \brief Returns a random real number from the range [a, b)
|
| 622 |
623 |
///
|
| 623 |
624 |
/// It returns a random real number from the range [a, b).
|
| 624 |
625 |
template <typename Number>
|
| 625 |
626 |
Number operator()(Number a, Number b) {
|
| 626 |
627 |
return real<Number>() * (b - a) + a;
|
| 627 |
628 |
}
|
| 628 |
629 |
|
| 629 |
630 |
/// \brief Returns a random integer from a range
|
| 630 |
631 |
///
|
| 631 |
632 |
/// It returns a random integer from the range {0, 1, ..., b - 1}.
|
| 632 |
633 |
template <typename Number>
|
| 633 |
634 |
Number integer(Number b) {
|
| 634 |
635 |
return _random_bits::Mapping<Number, Word>::map(core, b);
|
| 635 |
636 |
}
|
| 636 |
637 |
|
| 637 |
638 |
/// \brief Returns a random integer from a range
|
| 638 |
639 |
///
|
| 639 |
640 |
/// It returns a random integer from the range {a, a + 1, ..., b - 1}.
|
| 640 |
641 |
template <typename Number>
|
| 641 |
642 |
Number integer(Number a, Number b) {
|
| 642 |
643 |
return _random_bits::Mapping<Number, Word>::map(core, b - a) + a;
|
| 643 |
644 |
}
|
| 644 |
645 |
|
| 645 |
646 |
/// \brief Returns a random integer from a range
|
| 646 |
647 |
///
|
| 647 |
648 |
/// It returns a random integer from the range {0, 1, ..., b - 1}.
|
| 648 |
649 |
template <typename Number>
|
| 649 |
650 |
Number operator[](Number b) {
|
| 650 |
651 |
return _random_bits::Mapping<Number, Word>::map(core, b);
|
| 651 |
652 |
}
|
| 652 |
653 |
|
| 653 |
654 |
/// \brief Returns a random non-negative integer
|
| 654 |
655 |
///
|
| 655 |
656 |
/// It returns a random non-negative integer uniformly from the
|
| 656 |
657 |
/// whole range of the current \c Number type. The default result
|
| 657 |
658 |
/// type of this function is <tt>unsigned int</tt>.
|
| 658 |
659 |
template <typename Number>
|
| 659 |
660 |
Number uinteger() {
|
| 660 |
661 |
return _random_bits::IntConversion<Number, Word>::convert(core);
|
| 661 |
662 |
}
|
| 662 |
663 |
|
| 663 |
664 |
unsigned int uinteger() {
|
| 664 |
665 |
return uinteger<unsigned int>();
|
| 665 |
666 |
}
|
| 666 |
667 |
|
| 667 |
668 |
/// \brief Returns a random integer
|
| 668 |
669 |
///
|
| 669 |
670 |
/// It returns a random integer uniformly from the whole range of
|
| 670 |
671 |
/// the current \c Number type. The default result type of this
|
| 671 |
672 |
/// function is \c int.
|
| 672 |
673 |
template <typename Number>
|
| 673 |
674 |
Number integer() {
|
| 674 |
675 |
static const int nb = std::numeric_limits<Number>::digits +
|
| 675 |
676 |
(std::numeric_limits<Number>::is_signed ? 1 : 0);
|
| 676 |
677 |
return _random_bits::IntConversion<Number, Word, nb>::convert(core);
|
| 677 |
678 |
}
|
| 678 |
679 |
|
| 679 |
680 |
int integer() {
|
| 680 |
681 |
return integer<int>();
|
| 681 |
682 |
}
|
| 682 |
683 |
|
| 683 |
684 |
/// \brief Returns a random bool
|
| 684 |
685 |
///
|
| 685 |
686 |
/// It returns a random bool. The generator holds a buffer for
|
| 686 |
687 |
/// random bits. Every time when it become empty the generator makes
|
| 687 |
688 |
/// a new random word and fill the buffer up.
|
| 688 |
689 |
bool boolean() {
|
| 689 |
690 |
return bool_producer.convert(core);
|
| 690 |
691 |
}
|
| 691 |
692 |
|
| 692 |
693 |
///\name Non-uniform distributions
|
| 693 |
694 |
///
|
| 694 |
695 |
|
| 695 |
696 |
///@{
|
| 696 |
697 |
|
| 697 |
698 |
/// \brief Returns a random bool
|
| 698 |
699 |
///
|
| 699 |
700 |
/// It returns a random bool with given probability of true result.
|
| 700 |
701 |
bool boolean(double p) {
|
| 701 |
702 |
return operator()() < p;
|
| 702 |
703 |
}
|
| 703 |
704 |
|
| 704 |
705 |
/// Standard Gauss distribution
|
| 705 |
706 |
|
| 706 |
707 |
/// Standard Gauss distribution.
|
| 707 |
708 |
/// \note The Cartesian form of the Box-Muller
|
| 708 |
709 |
/// transformation is used to generate a random normal distribution.
|
| 709 |
710 |
/// \todo Consider using the "ziggurat" method instead.
|
| 710 |
711 |
double gauss()
|
| 711 |
712 |
{
|
| 712 |
713 |
double V1,V2,S;
|
| 713 |
714 |
do {
|
| 714 |
715 |
V1=2*real<double>()-1;
|
| 715 |
716 |
V2=2*real<double>()-1;
|
| 716 |
717 |
S=V1*V1+V2*V2;
|
| 717 |
718 |
} while(S>=1);
|
| 718 |
719 |
return std::sqrt(-2*std::log(S)/S)*V1;
|
| 719 |
720 |
}
|
| 720 |
721 |
/// Gauss distribution with given mean and standard deviation
|
| 721 |
722 |
|
| 722 |
723 |
/// Gauss distribution with given mean and standard deviation.
|
| 723 |
724 |
/// \sa gauss()
|
| 724 |
725 |
double gauss(double mean,double std_dev)
|
| 725 |
726 |
{
|
| 726 |
727 |
return gauss()*std_dev+mean;
|
| 727 |
728 |
}
|
| 728 |
729 |
|
| 729 |
730 |
/// Exponential distribution with given mean
|
| 730 |
731 |
|
| 731 |
732 |
/// This function generates an exponential distribution random number
|
| 732 |
733 |
/// with mean <tt>1/lambda</tt>.
|
| 733 |
734 |
///
|
| 734 |
735 |
double exponential(double lambda=1.0)
|
| 735 |
736 |
{
|
| 736 |
737 |
return -std::log(1.0-real<double>())/lambda;
|
| 737 |
738 |
}
|
| 738 |
739 |
|
| 739 |
740 |
/// Gamma distribution with given integer shape
|
| 740 |
741 |
|
| 741 |
742 |
/// This function generates a gamma distribution random number.
|
| 742 |
743 |
///
|
| 743 |
744 |
///\param k shape parameter (<tt>k>0</tt> integer)
|
| 744 |
745 |
double gamma(int k)
|
| 745 |
746 |
{
|
| 746 |
747 |
double s = 0;
|
| 747 |
748 |
for(int i=0;i<k;i++) s-=std::log(1.0-real<double>());
|
| 748 |
749 |
return s;
|
| 749 |
750 |
}
|
| 750 |
751 |
|
| 751 |
752 |
/// Gamma distribution with given shape and scale parameter
|
| 752 |
753 |
|
| 753 |
754 |
/// This function generates a gamma distribution random number.
|
| 754 |
755 |
///
|
| 755 |
756 |
///\param k shape parameter (<tt>k>0</tt>)
|
| 756 |
757 |
///\param theta scale parameter
|
| 757 |
758 |
///
|
| 758 |
759 |
double gamma(double k,double theta=1.0)
|
| 759 |
760 |
{
|
| 760 |
761 |
double xi,nu;
|
| 761 |
762 |
const double delta = k-std::floor(k);
|
| 762 |
|
const double v0=M_E/(M_E-delta);
|
|
763 |
const double v0=E/(E-delta);
|
| 763 |
764 |
do {
|
| 764 |
765 |
double V0=1.0-real<double>();
|
| 765 |
766 |
double V1=1.0-real<double>();
|
| 766 |
767 |
double V2=1.0-real<double>();
|
| 767 |
768 |
if(V2<=v0)
|
| 768 |
769 |
{
|
| 769 |
770 |
xi=std::pow(V1,1.0/delta);
|
| 770 |
771 |
nu=V0*std::pow(xi,delta-1.0);
|
| 771 |
772 |
}
|
| 772 |
773 |
else
|
| 773 |
774 |
{
|
| 774 |
775 |
xi=1.0-std::log(V1);
|
| 775 |
776 |
nu=V0*std::exp(-xi);
|
| 776 |
777 |
}
|
| 777 |
778 |
} while(nu>std::pow(xi,delta-1.0)*std::exp(-xi));
|
| 778 |
779 |
return theta*(xi-gamma(int(std::floor(k))));
|
| 779 |
780 |
}
|
| 780 |
781 |
|
| 781 |
782 |
/// Weibull distribution
|
| 782 |
783 |
|
| 783 |
784 |
/// This function generates a Weibull distribution random number.
|
| 784 |
785 |
///
|
| 785 |
786 |
///\param k shape parameter (<tt>k>0</tt>)
|
| 786 |
787 |
///\param lambda scale parameter (<tt>lambda>0</tt>)
|
| 787 |
788 |
///
|
| 788 |
789 |
double weibull(double k,double lambda)
|
| 789 |
790 |
{
|
| 790 |
791 |
return lambda*pow(-std::log(1.0-real<double>()),1.0/k);
|
| 791 |
792 |
}
|
| 792 |
793 |
|
| 793 |
794 |
/// Pareto distribution
|
| 794 |
795 |
|
| 795 |
796 |
/// This function generates a Pareto distribution random number.
|
| 796 |
797 |
///
|
| 797 |
798 |
///\param k shape parameter (<tt>k>0</tt>)
|
| 798 |
799 |
///\param x_min location parameter (<tt>x_min>0</tt>)
|
| 799 |
800 |
///
|
| 800 |
801 |
double pareto(double k,double x_min)
|
| 801 |
802 |
{
|
| 802 |
803 |
return exponential(gamma(k,1.0/x_min));
|
| 803 |
804 |
}
|
| 804 |
805 |
|
| 805 |
806 |
///@}
|
| 806 |
807 |
|
| 807 |
808 |
///\name Two dimensional distributions
|
| 808 |
809 |
///
|
| 809 |
810 |
|
| 810 |
811 |
///@{
|
| 811 |
812 |
|
| 812 |
813 |
/// Uniform distribution on the full unit circle
|
| 813 |
814 |
|
| 814 |
815 |
/// Uniform distribution on the full unit circle.
|
| 815 |
816 |
///
|
| 816 |
817 |
dim2::Point<double> disc()
|
| 817 |
818 |
{
|
| 818 |
819 |
double V1,V2;
|
| 819 |
820 |
do {
|
| 820 |
821 |
V1=2*real<double>()-1;
|
| 821 |
822 |
V2=2*real<double>()-1;
|
| 822 |
823 |
|
| 823 |
824 |
} while(V1*V1+V2*V2>=1);
|
| 824 |
825 |
return dim2::Point<double>(V1,V2);
|
| 825 |
826 |
}
|
| 826 |
827 |
/// A kind of two dimensional Gauss distribution
|
| 827 |
828 |
|
| 828 |
829 |
/// This function provides a turning symmetric two-dimensional distribution.
|
| 829 |
830 |
/// Both coordinates are of standard normal distribution, but they are not
|
| 830 |
831 |
/// independent.
|
| 831 |
832 |
///
|
| 832 |
833 |
/// \note The coordinates are the two random variables provided by
|
| 833 |
834 |
/// the Box-Muller method.
|
| 834 |
835 |
dim2::Point<double> gauss2()
|
| 835 |
836 |
{
|
| 836 |
837 |
double V1,V2,S;
|
| 837 |
838 |
do {
|
| 838 |
839 |
V1=2*real<double>()-1;
|
| 839 |
840 |
V2=2*real<double>()-1;
|
| 840 |
841 |
S=V1*V1+V2*V2;
|
| 841 |
842 |
} while(S>=1);
|
| 842 |
843 |
double W=std::sqrt(-2*std::log(S)/S);
|
| 843 |
844 |
return dim2::Point<double>(W*V1,W*V2);
|
| 844 |
845 |
}
|
| 845 |
846 |
/// A kind of two dimensional exponential distribution
|
| 846 |
847 |
|
| 847 |
848 |
/// This function provides a turning symmetric two-dimensional distribution.
|
| 848 |
849 |
/// The x-coordinate is of conditionally exponential distribution
|
| 849 |
850 |
/// with the condition that x is positive and y=0. If x is negative and
|
| 850 |
851 |
/// y=0 then, -x is of exponential distribution. The same is true for the
|
| 851 |
852 |
/// y-coordinate.
|
| 852 |
853 |
dim2::Point<double> exponential2()
|
| 853 |
854 |
{
|
| 854 |
855 |
double V1,V2,S;
|
| 855 |
856 |
do {
|
| 856 |
857 |
V1=2*real<double>()-1;
|
| 857 |
858 |
V2=2*real<double>()-1;
|
| 858 |
859 |
S=V1*V1+V2*V2;
|
| 859 |
860 |
} while(S>=1);
|
| 860 |
861 |
double W=-std::log(S)/S;
|
| 861 |
862 |
return dim2::Point<double>(W*V1,W*V2);
|
| 862 |
863 |
}
|
| 863 |
864 |
|
| 864 |
865 |
///@}
|
| 865 |
866 |
};
|
| 866 |
867 |
|
| 867 |
868 |
|
| 868 |
869 |
extern Random rnd;
|
| 869 |
870 |
|
| 870 |
871 |
}
|
| 871 |
872 |
|
| 872 |
873 |
#endif
|