mersenne.h

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// mersenne.h - written and placed in public domain by Jeffrey Walton.
//              Copyright assigned to Crypto++ project.

#ifndef CRYPTOPP_MERSENNE_TWISTER_H
#define CRYPTOPP_MERSENNE_TWISTER_H

#include "cryptlib.h"
#include "secblock.h"
#include "misc.h"

NAMESPACE_BEGIN(CryptoPP)

template <unsigned int K, unsigned int M, unsigned int N, unsigned int F, unsigned long S>
class MersenneTwister : public RandomNumberGenerator
{
public:
        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);
        }

        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: CRYPTOPP_ASSERT(0); ;;
                }

                // Wipe temp
                *((volatile word32*)&temp) = 0;
        }

        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;
        }

        void DiscardBytes(size_t n)
        {
                for(size_t i=0; i < RoundUpToMultipleOf(n, 4U); i++)
                        NextMersenneWord();
        }

protected:

        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);
        }

        void Twist()
        {
                static const unsigned long magic[2]={0x0UL, K};
                word32 kk, temp;

                CRYPTOPP_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:

        FixedSizeSecBlock<word32, N+1> m_state;
        unsigned int m_seed;
        unsigned int m_idx;
};

#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

#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