src/base/random_mt.cc

/*
 * A C-program for MT19937, with initialization improved 2002/1/26.
 * Coded by Takuji Nishimura and Makoto Matsumoto.
 *
 * Before using, initialize the state by using init_genrand(seed)
 * or init_by_array(init_key, key_length).
 *
 * 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.
 *
 *
 * Any feedback is very welcome.
 * http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html
 * email: m-mat @ math.sci.hiroshima-u.ac.jp (remove space)
 */

#include "base/random.hh"

/* initializes mt[N] with a seed */
void
Random::init(uint32_t s)
{
    mti = N + 1;
    mt[0] = s & (uint32_t)0xffffffff;

    for (mti = 1; mti < 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] &= (uint32_t)0xffffffff;
        /* for >32 bit machines */
    }
}

/* initialize by an array with array-length */
/* init_key is the array for initializing keys */
/* key_length is its length */
/* slight change for C++, 2004/2/26 */
void
Random::init(uint32_t init_key[], int key_length)
{
    int i = 1;
    int j = 0;
    int k = (N > key_length) ? N : key_length;

    init(19650218);

    for (; k; k--) {
        mt[i] = (mt[i] ^ ((mt[i-1] ^ (mt[i-1] >> 30)) * (uint32_t)1664525))
          + init_key[j] + j; /* non linear */

        mt[i] &= 0xffffffffUL; /* for WORDSIZE > 32 machines */

        i++;
        j++;

        if (i >= N) {
            mt[0] = mt[N - 1];
            i = 1;
        }

        if (j >= key_length)
            j = 0;
    }

    for (k = N - 1; k; k--) {
        /* non linear */
        mt[i] = (mt[i] ^ ((mt[i - 1] ^ (mt[i - 1] >> 30)) * 1566083941UL)) - i;

        /* for WORDSIZE > 32 machines */
        mt[i] &= (uint32_t)0xffffffff;
        i++;

        if (i >= N) {
            mt[0] = mt[N - 1];
            i = 1;
        }
    }

    /* MSB is 1; assuring non-zero initial array */
    mt[0] = (uint32_t)0x80000000;
}

/* generates a random number on [0,0xffffffff]-interval */
uint32_t
Random::genrand()
{
    uint32_t y;
    static uint32_t mag01[2] = { 0, MATRIX_A};

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

        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 & 0x1UL];
        }
        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 & 0x1UL];
        }

        y = mt[N - 1] & UPPER_MASK | mt[0] & LOWER_MASK;
        mt[N - 1] = mt[M - 1] ^ (y >> 1) ^ mag01[y & 0x1UL];

        mti = 0;
    }

    y = mt[mti++];

    /* Tempering */
    y ^= (y >> 11);
    y ^= (y << 7) & (uint32_t)0x9d2c5680;
    y ^= (y << 15) & (uint32_t)0xefc60000;
    y ^= (y >> 18);

    return y;
}