newrand.c

/* A C-program for MT19937: Integer     version                   */
/*  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.                     */

/* 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 NONZERO seed */
void
  sgenrand(seed)
    unsigned long seed;
{
      /* setting initial seeds to mt[N] using         */
      /* the generator Line 25 of Table 1 in          */
      /* [KNUTH 1981, The Art of Computer Programming */
      /*    Vol. 2 (2nd Ed.), pp102]                  */
      mt[0]= seed & 0xffffffff;
      for (mti=1; mti<N; mti++)
            mt[mti] = (69069 * mt[mti-1]) & 0xffffffff;
}

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; 
}