mersenne_inline.cpp

/* A C-program for MT19937: Real number version  (1998/4/6)    */
/*   genrand() generates one pseudorandom real number (double) */
/* which is uniformly distributed on [0,1]-interval, 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).     */
/* Integer generator is obtained by modifying two lines.       */
/*   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.                          */
 
#include <stdio.h>
#include <stdlib.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 int mt[N]; /* the array for the state vector  */
int mersenne_i = -1;       /*  < 0 means mt[N] is not initialized */
double mersenne_array[N];
 
/* initializing the array with a NONZERO seed */
void seed_mersenne(unsigned long seed) {
    int mti;
    /* 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]                  */
    if (seed % 2 == 0)
        seed++;
    mt[0] = seed & 0xffffffff;
    for (mti = 1; mti < N; mti++)
        mt[mti] = (69069 * mt[mti - 1]) & 0xffffffff;
 
    mersenne_i = 0;
}
 
double             /* generating reals */
/* unsigned int */ /* for integer generation */
mersenne_generate() {
    unsigned int y;
    int kk;
    static unsigned int mag01[2] = {0x0, MATRIX_A};
    /* mag01[x] = x * MATRIX_A  for x=0,1 */
 
    if (mersenne_i < 0) { /* if sgenrand() has not been called, */
        printf("DUMMY: you did not seed the generator!\n");
        exit(1);
    }
 
    /* generate N words at one time */
 
    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];
 
    for (kk = 0; kk < N; kk++) {
        y = mt[kk];
        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);
        mersenne_array[kk] =
            (double)y * 2.3283064365386963e-10; /* reals: interval [0,1) */
    }
 
    mersenne_i = N;
    return (mersenne_array[--mersenne_i]);
    /* return y; */ /* for integer generation */
}