mt19937ar.c

/*
 * Copyright (C) 1997 - 2002, Makoto Matsumoto and Takuji Nishimura,
 * 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 AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <stdio.h>

/* Period parameters */
#define MT_N 624
#define MT_M 397
#define MT_MATRIX_A 0x9908b0dfUL        /**< constant vector a */
#define MT_UPPER_MASK 0x80000000UL      /**< most significant w-r bits */
#define MT_LOWER_MASK 0x7fffffffUL      /**< least significant r bits */

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

/**
 * initializes mt[MT_N] with a seed
 */
static void init_genrand(unsigned long s) {
    mt[0] = s & 0xffffffffUL;
    for (mti = 1; mti < MT_N; 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
 */
static unsigned long genrand_int32(void) {
    unsigned long y;
    static unsigned long mag01[2] = { 0x0UL, MT_MATRIX_A };
    /* mag01[x] = x * MT_MATRIX_A  for x=0,1 */

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

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

        for (kk = 0; kk < MT_N - MT_M; kk++) {
            y = (mt[kk] & MT_UPPER_MASK) | (mt[kk + 1] & MT_LOWER_MASK);
            mt[kk] = mt[kk + MT_M] ^ (y >> 1) ^ mag01[y & 0x1UL];
        }
        for (; kk < MT_N - 1; kk++) {
            y = (mt[kk] & MT_UPPER_MASK) | (mt[kk + 1] & MT_LOWER_MASK);
            mt[kk] = mt[kk + (MT_M - MT_N)] ^ (y >> 1) ^ mag01[y & 0x1UL];
        }
        y = (mt[MT_N - 1] & MT_UPPER_MASK) | (mt[0] & MT_LOWER_MASK);
        mt[MT_N - 1] = mt[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) with 53-bit resolution
 */
static double genrand_res53(void) {
    unsigned long a = genrand_int32() >> 5, b = genrand_int32() >> 6;
    return (1.0 * a * 67108864.0 + b) * (1.0 / 9007199254740992.0);
}

#undef MT_N
#undef MT_M
#undef MT_MATRIX_A
#undef MT_UPPER_MASK
#undef MT_LOWER_MASK

/*
 * non-static original content
 */

/** @file mt19937ar.c
 * @brief Mersenne Twister pseudo-RNG code
 *
 * This is the original code by Takuji Nishimura and Makoto Matsumoto,
 * amended to keep only the parts used.
 * Source : http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html
 *
 * @author Makoto Matsumoto (1997 - 2002)
 * @author Takuji Nishimura (1997 - 2002)
 *
 */

/* ensure consistency */
#include "mt19937ar.h"

/* string tag inserted into the binary, helps tracking versions */
char _mt19937ar_tag[] = "using mt19937ar " MT19937AR_VERSION;

/**
 * @brief initializes the generator with a seed
 */
void mt_init_genrand(unsigned long s) {
    init_genrand(s);
    return;
}

/**
 * @brief generates a random number on [0,1) with 53-bit resolution
 */
double mt_genrand_res53(void) {
    return genrand_res53();
}