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/**************************************************************************
*
* Copyright 2012 VMware, Inc.
* All Rights Reserved.
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sub license, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice (including the
* next paragraph) shall be included in all copies or substantial portions
* of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
* OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
* IN NO EVENT SHALL VMWARE AND/OR ITS SUPPLIERS BE LIABLE FOR
* ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*
**************************************************************************/
#ifndef MERSENNE_HPP
#define MERSENNE_HPP
#include <string>
#include <stdio.h>
#include <stdint.h>
/**
* Variant of Mersenne Twister which can be skipped to any point in time.
*
* Instead of producing a new state table by mutating the previous table it initiates
* again using a seed which is the last random value of the previous state
*/
class Mersenne
{
public:
static const uint32_t n = 624;
static const uint32_t m = 397;
static const uint32_t b32 = 1 << 31;
static const uint32_t rand_max = 0xFFFFFFFF;
public:
Mersenne() :
mSeed(0), mIndex(0), mState()
{
}
Mersenne(unsigned int seed)
{
init(seed);
}
unsigned int value()
{
uint32_t x = mState[mIndex++];
x ^= (x >> 11);
x ^= (x << 7) & 0x9D2C5680;
x ^= (x << 15) & 0xEFC60000;
x ^= (x >> 18);
if (mIndex == n){
init(x);
return value();
}
return x;
}
unsigned int max()
{
return 0xFFFFFFFF;
}
std::string state()
{
char buffer[32];
sprintf(buffer, "%08x%03d", mSeed, mIndex);
return buffer;
}
void setState(const std::string& state){
uint32_t seed, index;
sscanf(state.c_str(), "%08x%03d", &seed, &index);
init(seed);
mIndex = index;
}
void init(uint32_t seed)
{
mIndex = 0;
mSeed = seed;
/* Standard MT initialiser */
mState[0] = seed;
for (uint32_t i = 1; i < n; ++i)
mState[i] = 1812433253 * (mState[i - 1] ^ (mState[i - 1] >> 30)) + i;
/* Standard MT number generator, split into parts to avoid having to do % n */
for (uint32_t i = 0; i < (n - m); ++i)
mState[i] = mState[i + m] ^ twist(mState[i], mState[i + 1]);
for (uint32_t i = n - m; i < (n - 1); ++i)
mState[i] = mState[i + m - n] ^ twist(mState[i], mState[i + 1]);
mState[n - 1] = mState[m - 1] ^ twist(mState[n - 1], mState[0]);
}
private:
inline uint32_t twist(uint32_t a, uint32_t b)
{
return (((a & b32) | (b & ~b32)) >> 1) ^ ((b & 1) ? 0x9908B0DF : 0);
}
private:
uint32_t mSeed;
uint32_t mIndex;
uint32_t mState[n];
};
#endif // MERSENNE_HPP
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