RandGen.h

/* A C-program for MT19937: Integer version (1998/4/6)            */
/*  genrand() generates one pseudorandom unsigned integer (32bit) */
/* which is uniformly distributed among 0 to 2^32-1  for each     */
/* call. sgenrand(seed) set initial values to the working area    */
/* of 624 words. Before genrand(), sgenrand(seed) must be         */
/* called once. (seed is any 32-bit integer except for 0).        */
/*   Coded by Takuji Nishimura, considering the suggestions by    */
/* Topher Cooper and Marc Rieffel in July-Aug. 1997.              */

/* This library is free software; you can redistribute it and/or   */
/* modify it under the terms of the GNU Library General Public     */
/* License as published by the Free Software Foundation; either    */
/* version 2 of the License, or (at your option) any later         */
/* version.                                                        */
/* This library is distributed in the hope that it will be useful, */
/* but WITHOUT ANY WARRANTY; without even the implied warranty of  */
/* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.            */
/* See the GNU Library General Public License for more details.    */
/* You should have received a copy of the GNU Library General      */
/* Public License along with this library; if not, write to the    */
/* Free Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA   */
/* 02111-1307  USA                                                 */

/* Copyright (C) 1997 Makoto Matsumoto and Takuji Nishimura.       */
/* When you use this, send an email to: matumoto@math.keio.ac.jp   */
/* with an appropriate reference to your work.                     */

/* REFERENCE                                                       */
/* M. Matsumoto and T. Nishimura,                                  */
/* "Mersenne Twister: A 623-Dimensionally Equidistributed Uniform  */
/* Pseudo-Random Number Generator",                                */
/* ACM Transactions on Modeling and Computer Simulation,           */
/* Vol. 8, No. 1, January 1998, pp 3--30.                          */

/* Period parameters */
#define N 624
#define M 397
#define MATRIX_A 0x9908b0df   /* constant vector a */
#define UPPER_MASK 0x80000000 /* most significant w-r bits */
#define LOWER_MASK 0x7fffffff /* least significant r bits */

/* Tempering parameters */
#define TEMPERING_MASK_B 0x9d2c5680
#define TEMPERING_MASK_C 0xefc60000
#define TEMPERING_SHIFT_U(y)  (y >> 11)
#define TEMPERING_SHIFT_S(y)  (y << 7)
#define TEMPERING_SHIFT_T(y)  (y << 15)
#define TEMPERING_SHIFT_L(y)  (y >> 18)

class RandGen {
  private:
  unsigned long mt[N]; /* the array for the state vector  */
  int mti;

  public:
  RandGen() : mti(N+1) {
    mag01[0]=0x0;
    mag01[1] = MATRIX_A;
  }

  /* initializing the array with a NONZERO seed */
  void sgenrand(unsigned long seed);
  unsigned long mag01[2];

  unsigned long genrand()
  {
    unsigned long y;

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

      /*if (mti == N+1)   // if sgenrand() has not been called,
	sgenrand(4357); // a default initial seed is used
      */

      for (kk=0;kk<N-M;kk++) {
	y = (mt[kk]&UPPER_MASK)|(mt[kk+1]&LOWER_MASK);
	mt[kk] = mt[kk+M] ^ (y >> 1) ^ mag01[y & 0x1];
      }
      for (;kk<N-1;kk++) {
	y = (mt[kk]&UPPER_MASK)|(mt[kk+1]&LOWER_MASK);
	mt[kk] = mt[kk+(M-N)] ^ (y >> 1) ^ mag01[y & 0x1];
      }
      y = (mt[N-1]&UPPER_MASK)|(mt[0]&LOWER_MASK);
      mt[N-1] = mt[M-1] ^ (y >> 1) ^ mag01[y & 0x1];

      mti = 0;
    }

    y = mt[mti++];
    y ^= TEMPERING_SHIFT_U(y);
    y ^= TEMPERING_SHIFT_S(y) & TEMPERING_MASK_B;
    y ^= TEMPERING_SHIFT_T(y) & TEMPERING_MASK_C;
    y ^= TEMPERING_SHIFT_L(y);

    return y;
  }
};