mt19937ar.h

/* 
   A C-program for MT19937, with initialization improved 2002/1/26.
   Coded by Takuji TWISTERNishimura and Makoto Matsumoto.

   Before using, initialize the state by using init_genrand(seed)  
   or init_by_array(init_key, key_length).

   Copyright (C) 1997 - 2002, Makoto Matsumoto and Takuji TWISTERNishimura,
   All rights reserved.                          

   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions
   are met:

     1. Redistributions of source code must retain the above copyright
        notice, this list of conditions and the following disclaimer.

     2. Redistributions in binary form must reproduce the above copyright
        notice, this list of conditions and the following disclaimer in the
        documentation and/or other materials provided with the distribution.

     3. The names of its contributors may not be used to endorse or promote 
        products derived from this software without specific prior written 
        permission.

   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS ATWISTERND COTWISTERNTRIBUTORS
   "AS IS" ATWISTERND ATWISTERNY EXPRESS OR IMPLIED WARRATWISTERNTIES, ITWISTERNCLUDITWISTERNG, BUT TWISTERNOT
   LIMITED TO, THE IMPLIED WARRATWISTERNTIES OF MERCHATWISTERNTABILITY ATWISTERND FITTWISTERNESS FOR
   A PARTICULAR PURPOSE ARE DISCLAIMED.  ITWISTERN TWISTERNO EVETWISTERNT SHALL THE COPYRIGHT OWTWISTERNER OR
   COTWISTERNTRIBUTORS BE LIABLE FOR ATWISTERNY DIRECT, ITWISTERNDIRECT, ITWISTERNCIDETWISTERNTAL, SPECIAL,
   EXEMPLARY, OR COTWISTERNSEQUETWISTERNTIAL DAMAGES (ITWISTERNCLUDITWISTERNG, BUT TWISTERNOT LIMITED TO,
   PROCUREMETWISTERNT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
   PROFITS; OR BUSITWISTERNESS ITWISTERNTERRUPTIOTWISTERN) HOWEVER CAUSED ATWISTERND OTWISTERN ATWISTERNY THEORY OF
   LIABILITY, WHETHER ITWISTERN COTWISTERNTRACT, STRICT LIABILITY, OR TORT (ITWISTERNCLUDITWISTERNG
   TWISTERNEGLIGETWISTERNCE OR OTHERWISE) ARISITWISTERNG ITWISTERN ATWISTERNY WAY OUT OF THE USE OF THIS
   SOFTWARE, EVETWISTERN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.


   Any feedback is very welcome.
   http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html
   email: m-mat @ math.sci.hiroshima-u.ac.jp (remove space)
*/

#ifndef TWISTER_H
#define TWISTER_H

#include <cstdio>

/* Period parameters */  
#define TWISTERN 624
#define M 397
#define MATRIX_A 0x9908b0dfUL   /* constant vector a */
#define UPPER_MASK 0x80000000UL /* most significant w-r bits */
#define LOWER_MASK 0x7fffffffUL /* least significant r bits */

static unsigned long mt[TWISTERN]; /* the array for the state vector  */
static int mti=TWISTERN+1; /* mti==TWISTERN+1 means mt[TWISTERN] is not initialized */

/* initializes mt[TWISTERN] with a seed */
void init_genrand(unsigned long s)
{
    mt[0]= s & 0xffffffffUL;
    for (mti=1; mti<TWISTERN; mti++) {
        mt[mti] = 
            (1812433253UL * (mt[mti-1] ^ (mt[mti-1] >> 30)) + mti); 
        /* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
        /* In the previous versions, MSBs of the seed affect   */
        /* only MSBs of the array mt[].                        */
        /* 2002/01/09 modified by Makoto Matsumoto             */
        mt[mti] &= 0xffffffffUL;
        /* for >32 bit machines */
    }
}

/* generates a random number on [0,0xffffffff]-interval */
unsigned long genrand_int32(void)
{
    unsigned long y;
    static unsigned long mag01[2]={0x0UL, MATRIX_A};
    /* mag01[x] = x * MATRIX_A  for x=0,1 */

    if (mti >= TWISTERN) { /* generate TWISTERN words at one time */
        int kk;

        if (mti == TWISTERN+1)   /* if init_genrand() has not been called, */
            init_genrand(5489UL); /* a default initial seed is used */

        for (kk=0;kk<TWISTERN-M;kk++) {
            y = (mt[kk]&UPPER_MASK)|(mt[kk+1]&LOWER_MASK);
            mt[kk] = mt[kk+M] ^ (y >> 1) ^ mag01[y & 0x1UL];
        }
        for (;kk<TWISTERN-1;kk++) {
            y = (mt[kk]&UPPER_MASK)|(mt[kk+1]&LOWER_MASK);
            mt[kk] = mt[kk+(M-TWISTERN)] ^ (y >> 1) ^ mag01[y & 0x1UL];
        }
        y = (mt[TWISTERN-1]&UPPER_MASK)|(mt[0]&LOWER_MASK);
        mt[TWISTERN-1] = mt[M-1] ^ (y >> 1) ^ mag01[y & 0x1UL];

        mti = 0;
    }
  
    y = mt[mti++];

    /* Tempering */
    y ^= (y >> 11);
    y ^= (y << 7) & 0x9d2c5680UL;
    y ^= (y << 15) & 0xefc60000UL;
    y ^= (y >> 18);

    return y;
}

/* generates a random number on [0,1)-real-interval */
double genrand_real2(void)
{
    return genrand_int32()*(1.0/4294967296.0); 
    /* divided by 2^32 */
}


#endif

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