mersenne.h
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// mersenne.h - written and placed in public domain by Jeffrey Walton.
// Copyright assigned to Crypto++ project.
//! \file mersenne.h
//! \brief Class file for Mersenne Twister
//! \warning MersenneTwister is suitable for Monte-Carlo simulations, where uniformaly distrubuted
//! numbers are required quickly. It should not be used for cryptographic purposes.
//! \since Crypto++ 5.6.3
#ifndef CRYPTOPP_MERSENNE_TWISTER_H
#define CRYPTOPP_MERSENNE_TWISTER_H
#include "cryptlib.h"
#include "secblock.h"
#include "misc.h"
NAMESPACE_BEGIN(CryptoPP)
//! \class MersenneTwister
//! \brief Mersenne Twister class for Monte-Carlo simulations
//! \tparam K Magic constant
//! \tparam M Period parameter
//! \tparam N Size of the state vector
//! \tparam F Multiplier constant
//! \tparam S Initial seed
//! \details Provides the MersenneTwister implementation. The class is a header-only implementation.
//! \warning MersenneTwister is suitable for simulations, where uniformaly distrubuted numbers are
//! required quickly. It should not be used for cryptographic purposes.
//! \sa MT19937, MT19937ar
//! \since Crypto++ 5.6.3
template <unsigned int K, unsigned int M, unsigned int N, unsigned int F, unsigned long S>
class MersenneTwister : public RandomNumberGenerator
{
public:
//! \brief Construct a Mersenne Twister
//! \param seed 32-bit seed
//! \details Defaults to template parameter S due to changing algorithm
//! parameters over time
MersenneTwister(unsigned long seed = S) : m_seed(seed), m_idx(N)
{
m_state[0] = seed;
for (unsigned int i = 1; i < N+1; i++)
m_state[i] = word32(F * (m_state[i-1] ^ (m_state[i-1] >> 30)) + i);
}
//! \brief Generate random array of bytes
//! \param output byte buffer
//! \param size length of the buffer, in bytes
//! \details Bytes are written to output in big endian order. If output length
//! is not a multiple of word32, then unused bytes are not accumulated for subsequent
//! calls to GenerateBlock. Rather, the unused tail bytes are discarded, and the
//! stream is continued at the next word32 boundary from the state array.
void GenerateBlock(byte *output, size_t size)
{
// Handle word32 size blocks
word32 temp;
for (size_t i=0; i < size/4; i++, output += 4)
{
#if defined(CRYPTOPP_ALLOW_UNALIGNED_DATA_ACCESS) && defined(IS_LITTLE_ENDIAN)
*((word32*)output) = ByteReverse(NextMersenneWord());
#elif defined(CRYPTOPP_ALLOW_UNALIGNED_DATA_ACCESS)
*((word32*)output) = NextMersenneWord();
#else
temp = NextMersenneWord();
output[3] = CRYPTOPP_GET_BYTE_AS_BYTE(temp, 0);
output[2] = CRYPTOPP_GET_BYTE_AS_BYTE(temp, 1);
output[1] = CRYPTOPP_GET_BYTE_AS_BYTE(temp, 2);
output[0] = CRYPTOPP_GET_BYTE_AS_BYTE(temp, 3);
#endif
}
// No tail bytes
if (size%4 == 0)
{
// Wipe temp
*((volatile word32*)&temp) = 0;
return;
}
// Handle tail bytes
temp = NextMersenneWord();
switch (size%4)
{
case 3: output[2] = CRYPTOPP_GET_BYTE_AS_BYTE(temp, 1); /* fall through */
case 2: output[1] = CRYPTOPP_GET_BYTE_AS_BYTE(temp, 2); /* fall through */
case 1: output[0] = CRYPTOPP_GET_BYTE_AS_BYTE(temp, 3); break;
default: assert(0); ;;
}
// Wipe temp
*((volatile word32*)&temp) = 0;
}
//! \brief Generate a random 32-bit word in the range min to max, inclusive
//! \returns random 32-bit word in the range min to max, inclusive
//! \details If the 32-bit candidate is not within the range, then it is discarded
//! and a new candidate is used.
word32 GenerateWord32(word32 min=0, word32 max=0xffffffffL)
{
const word32 range = max-min;
if (range == 0xffffffffL)
return NextMersenneWord();
const int maxBits = BitPrecision(range);
word32 value;
do{
value = Crop(NextMersenneWord(), maxBits);
} while (value > range);
return value+min;
}
//! \brief Generate and discard n bytes
//! \param n the number of bytes to discard, rounded up to a <tt>word32</tt> size
//! \details If n is not a multiple of <tt>word32</tt>, then unused bytes are
//! not accumulated for subsequent calls to GenerateBlock. Rather, the unused
//! tail bytes are discarded, and the stream is continued at the next
//! <tt>word32</tt> boundary from the state array.
void DiscardBytes(size_t n)
{
for(size_t i=0; i < RoundUpToMultipleOf(n, 4U); i++)
NextMersenneWord();
}
protected:
//! \brief Returns the next 32-bit word from the state array
//! \returns the next 32-bit word from the state array
//! \details fetches the next word frm the state array, performs bit operations on
//! it, and then returns the value to the caller.
word32 NextMersenneWord()
{
if (m_idx >= N) { Twist(); }
word32 temp = m_state[m_idx++];
temp ^= (temp >> 11);
temp ^= (temp << 7) & 0x9D2C5680; // 0x9D2C5680 (2636928640)
temp ^= (temp << 15) & 0xEFC60000; // 0xEFC60000 (4022730752)
return temp ^ (temp >> 18);
}
//! \brief Performs the twist operaton on the state array
void Twist()
{
static const unsigned long magic[2]={0x0UL, K};
word32 kk, temp;
assert(N >= M);
for (kk=0;kk<N-M;kk++)
{
temp = (m_state[kk] & 0x80000000)|(m_state[kk+1] & 0x7FFFFFFF);
m_state[kk] = m_state[kk+M] ^ (temp >> 1) ^ magic[temp & 0x1UL];
}
for (;kk<N-1;kk++)
{
temp = (m_state[kk] & 0x80000000)|(m_state[kk+1] & 0x7FFFFFFF);
m_state[kk] = m_state[kk+(M-N)] ^ (temp >> 1) ^ magic[temp & 0x1UL];
}
temp = (m_state[N-1] & 0x80000000)|(m_state[0] & 0x7FFFFFFF);
m_state[N-1] = m_state[M-1] ^ (temp >> 1) ^ magic[temp & 0x1UL];
// Reset index
m_idx = 0;
// Wipe temp
*((volatile word32*)&temp) = 0;
}
private:
//! \brief 32-bit word state array of size N
FixedSizeSecBlock<word32, N+1> m_state;
//! \brief the value used to seed the generator
unsigned int m_seed;
//! \brief the current index into the state array
unsigned int m_idx;
};
//! \class MT19937
//! \brief Original MT19937 generator provided in the ACM paper.
//! \details MT19937 uses 4537 as default initial seed.
//! \sa MT19937ar, <A HREF="http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/ARTICLES/mt.pdf">Mersenne twister:
//! a 623-dimensionally equidistributed uniform pseudo-random number generator</A>
//! \since Crypto++ 5.6.3
#if CRYPTOPP_DOXYGEN_PROCESSING
class MT19937 : public MersenneTwister<0x9908B0DF /*2567483615*/, 397, 624, 0x10DCD /*69069*/, 4537> {};
#else
typedef MersenneTwister<0x9908B0DF /*2567483615*/, 397, 624, 0x10DCD /*69069*/, 4537> MT19937;
#endif
//! \class MT19937ar
//! \brief Updated MT19937 generator adapted to provide an array for initialization.
//! \details MT19937 uses 5489 as default initial seed. Use this generator when interoperating with C++11's
//! mt19937 class.
//! \sa MT19937, <A HREF="http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/MT2002/emt19937ar.html">Mersenne Twister
//! with improved initialization</A>
//! \since Crypto++ 5.6.3
#if CRYPTOPP_DOXYGEN_PROCESSING
class MT19937ar : public MersenneTwister<0x9908B0DF /*2567483615*/, 397, 624, 0x6C078965 /*1812433253*/, 5489> {};
#else
typedef MersenneTwister<0x9908B0DF /*2567483615*/, 397, 624, 0x6C078965 /*1812433253*/, 5489> MT19937ar;
#endif
NAMESPACE_END
#endif // CRYPTOPP_MERSENNE_TWISTER_H
MersenneTwister::MersenneTwister
MersenneTwister(unsigned long seed=S)
Construct a Mersenne Twister.
Definition: mersenne.h:38
RoundUpToMultipleOf
T1 RoundUpToMultipleOf(const T1 &n, const T2 &m)
Rounds a value up to a multiple of a second value.
Definition: misc.h:865
MT19937ar
Updated MT19937 generator adapted to provide an array for initialization.
Definition: mersenne.h:204
secblock.h
Classes and functions for secure memory allocations.
MersenneTwister::DiscardBytes
void DiscardBytes(size_t n)
Generate and discard n bytes.
Definition: mersenne.h:120
RandomNumberGenerator
Interface for random number generators.
Definition: cryptlib.h:1186
MersenneTwister
Mersenne Twister class for Monte-Carlo simulations.
Definition: mersenne.h:31
misc.h
Utility functions for the Crypto++ library.
MT19937
Original MT19937 generator provided in the ACM paper.
Definition: mersenne.h:191
BitPrecision
unsigned int BitPrecision(const T &value)
Returns the number of bits required for a value.
Definition: misc.h:645
FixedSizeSecBlock< word32, N+1 >
ByteReverse
byte ByteReverse(byte value)
Reverses bytes in a 8-bit value.
Definition: misc.h:1705
MersenneTwister::GenerateBlock
void GenerateBlock(byte *output, size_t size)
Generate random array of bytes.
Definition: mersenne.h:52
Crop
T Crop(T value, size_t bits)
Truncates the value to the specified number of bits.
Definition: misc.h:728
CryptoPP
Crypto++ library namespace.
MersenneTwister::GenerateWord32
word32 GenerateWord32(word32 min=0, word32 max=0xffffffffL)
Generate a random 32-bit word in the range min to max, inclusive.
Definition: mersenne.h:98
cryptlib.h
Abstract base classes that provide a uniform interface to this library.