mt19937int.c

/* A C-program for MT19937: Integer version (1999/10/28)          */
/*  genrand() generates one pseudorandom unsigned integer (32bit) */
/* which is uniformly distributed among 0 to 2^32-1  for each     */
/* call. sgenrand(seed) sets initial values to the working area   */
/* of 624 words. Before genrand(), sgenrand(seed) must be         */
/* called once. (seed is any 32-bit integer.)                     */
/*   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, 1999 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.                          */

#include<stdio.h>

/* 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)

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

/* Initializing the array with a seed */
void
sgenrand(seed)
unsigned long seed;
{
   int i;

   for (i=0;i<N;i++)
   {
      mt[i] = seed & 0xffff0000;
      seed = 69069 * seed + 1;
      mt[i] |= (seed & 0xffff0000) >> 16;
      seed = 69069 * seed + 1;
   }
   mti = N;
}

/* Initialization by "sgenrand()" is an example. Theoretically,      */
/* there are 2^19937-1 possible states as an intial state.           */
/* This function allows to choose any of 2^19937-1 ones.             */
/* Essential bits in "seed_array[]" is following 19937 bits:         */
/*  (seed_array[0]&UPPER_MASK), seed_array[1], ..., seed_array[N-1]. */
/* (seed_array[0]&LOWER_MASK) is discarded.                          */
/* Theoretically,                                                    */
/*  (seed_array[0]&UPPER_MASK), seed_array[1], ..., seed_array[N-1]  */
/* can take any values except all zeros.                             */
void
lsgenrand(seed_array)
unsigned long seed_array[];
/* the length of seed_array[] must be at least N */
{
   int i;

   for (i=0;i<N;i++)
      mt[i] = seed_array[i];
   mti=N;
}

unsigned long
genrand()
{
   unsigned long y;
   static unsigned long mag01[2]={0x0, MATRIX_A};
   /* mag01[x] = x * MATRIX_A  for x=0,1 */

   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;
}

/* This main() outputs first 1000 generated numbers.  */
#if 0
main()
{
   int i;

   sgenrand(4357);
   for (i=0; i<1000; i++)
   {
      printf("%10lu ", genrand());
      if (i%5==4) printf("\n");
   }
}
#endif