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  MersenneTwister
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MersenneTwister is a fast (below 40 cycles of x86 CPU) pseudorandom number generator with very strong cryptographics properties and VERY large period (2^19937 -1).


Download Associated File: cMersenneTwister.h (3,827 bytes)

#ifndef cMersenneTwister_h_INCLUDED
#define cMersenneTwister_h_INCLUDED

// This is the ``Mersenne Twister'' random number generator MT19937, // which generates pseudorandom integers uniformly distributed in // 0..(2^32 - 1) starting from any odd seed in 0..(2^32 - 1) with // period 2^19937 -1 with 623-dimmensional equidistibution up to // 32-bits of accurancy. // This is Shaw Cookus Implementation of algorithm invented by // Takuji Nishimura embedded into C++ class by me, that is // Maciek Urbański. // Amortized cost of generating 32-bit integer is 33 CPU cycles on // my K6-2 450MHz (MSVC 6.0/SP4). It's fast. ;-) // For detailed properties - there is a paper: "Mersenne Twister: // A 623-dimmensionally equidstributed uniform pseudorandom number // generator" by Makoto Matsumoto and Takuji Nishimura. #define N (624) #define M (397) #define K (0x9908B0DFU) #define hiBit(u) ((u) & 0x80000000U) #define loBit(u) ((u) & 0x00000001U) #define loBits(u) ((u) & 0x7FFFFFFFU) #define mixBits(u, v) (hiBit(u)|loBits(v)) #define SEED0 (4357U)

class cMersenneTwister { private: unsigned long state[N+1]; // state vector unsigned long *next; // next random int left; // how many values left public: //////////////////////////////////////////////////////////////////// // initialize MT via linear conguential generator // x[n+1] = (69069 * x[n]) mod 2^32 void Init( unsigned long seed //32-bit seed ) { register unsigned long x = (seed | 1U) & 0xFFFFFFFFU, *s = state; register int j; for( left=0, *s++=x, j=N; --j; *s++ = (x*=69069U) & 0xFFFFFFFFU); } //////////////////////////////////////////////////////////////////// // load state vector void Load( unsigned long *state //pointer to state (624*4 bytes) ) { register unsigned long j, *s = state; for( j=N; --j; *s++ = *state++ ); } //////////////////////////////////////////////////////////////////// // save state vector void Save( unsigned long *state //pointer to state (624*4 bytes) ) { register unsigned long j, *s = state; for( j=N; --j; *state++ = *s++ ); } //////////////////////////////////////////////////////////////////// // create MT object cMersenneTwister( void ) { left = -1; } //////////////////////////////////////////////////////////////////// // create MT object & init it cMersenneTwister( unsigned long seed ) { Init( seed ); } //////////////////////////////////////////////////////////////////// // create MT object & load seed cMersenneTwister( unsigned long *state ) { Load( state ); } //////////////////////////////////////////////////////////////////// // calculates next values unsigned long Reload( void ) { register unsigned long *p0=state, *p2=state+2, *pM=state+M, s0, s1; register int j; if(left < -1) Init( SEED0 ); left=N-1, next=state+1; for( s0=state[0], s1=state[1], j=N-M+1; --j; s0=s1, s1=*p2++ ) *p0++ = *pM++ ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U); for(pM=state, j=M; --j; s0=s1, s1=*p2++) *p0++ = *pM++ ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U); s1 = state[0], *p0 = *pM ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U); s1 ^= (s1 >> 11); s1 ^= (s1 << 7) & 0x9D2C5680U; s1 ^= (s1 << 15) & 0xEFC60000U; return ( s1 ^ (s1 >> 18) ); } //////////////////////////////////////////////////////////////////// // get next value inline unsigned long Random( void ) { register unsigned long y; if(--left < 0) return Reload(); y = *next++; y ^= (y >> 11); y ^= (y << 7) & 0x9D2C5680U; y ^= (y << 15) & 0xEFC60000U; return(y ^ (y >> 18)); } };

#endif

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