/mt.c

/*
 * This is based on trimmed version of MT19937.  To get the original version,
 * contact <http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html>.
 * 
 * The original copyright notice follows.
 * 
 * A C-program for MT19937, with initialization improved 2002/2/10.
 * Coded by Takuji Nishimura and Makoto Matsumoto.
 * This is a faster version by taking Shawn Cokus's optimization,
 * Matthe Bellew's simplification, Isaku Wada's real version.
 * 
 * Before using, initialize the state by using init_genrand(mt, seed)
 * or init_by_array(mt, 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.keio.ac.jp/matumoto/emt.html
 * email: matumoto@math.keio.ac.jp
 */

#include <limits.h>
typedef int int_must_be_32bit_at_least[sizeof(int) * CHAR_BIT < 32 ? -1 : 1];

/* Period parameters */
#define N 624
#define M 397
#define MATRIX_A 0x9908b0dfU	/* constant vector a */
#define UMASK 0x80000000U	/* most significant w-r bits */
#define LMASK 0x7fffffffU	/* least significant r bits */
#define MIXBITS(u,v) ( ((u) & UMASK) | ((v) & LMASK) )
#define TWIST(u,v) ((MIXBITS(u,v) >> 1) ^ ((v)&1U ? MATRIX_A : 0U))

enum {MT_MAX_STATE = N};

struct MT {
    /* assume int is enough to store 32bits */
    unsigned int state[N]; /* the array for the state vector  */
    unsigned int *next;
    int left;
};

#define genrand_initialized(mt) ((mt)->next != 0)
#define uninit_genrand(mt) ((mt)->next = 0)

/* initializes state[N] with a seed */
static void
init_genrand(struct MT *mt, unsigned int s)
{
    int j;
    mt->state[0] = s & 0xffffffffU;
    for (j=1; j<N; j++) {
        mt->state[j] = (1812433253U * (mt->state[j-1] ^ (mt->state[j-1] >> 30)) + j);
        /* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
        /* In the previous versions, MSBs of the seed affect   */
        /* only MSBs of the array state[].                     */
        /* 2002/01/09 modified by Makoto Matsumoto             */
        mt->state[j] &= 0xffffffff;  /* for >32 bit machines */
    }
    mt->left = 1;
    mt->next = mt->state + N;
}

/* 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 */
static void
init_by_array(struct MT *mt, unsigned int init_key[], int key_length)
{
    int i, j, k;
    init_genrand(mt, 19650218U);
    i=1; j=0;
    k = (N>key_length ? N : key_length);
    for (; k; k--) {
        mt->state[i] = (mt->state[i] ^ ((mt->state[i-1] ^ (mt->state[i-1] >> 30)) * 1664525U))
          + init_key[j] + j; /* non linear */
        mt->state[i] &= 0xffffffffU; /* for WORDSIZE > 32 machines */
        i++; j++;
        if (i>=N) { mt->state[0] = mt->state[N-1]; i=1; }
        if (j>=key_length) j=0;
    }
    for (k=N-1; k; k--) {
        mt->state[i] = (mt->state[i] ^ ((mt->state[i-1] ^ (mt->state[i-1] >> 30)) * 1566083941U))
          - i; /* non linear */
        mt->state[i] &= 0xffffffffU; /* for WORDSIZE > 32 machines */
        i++;
        if (i>=N) { mt->state[0] = mt->state[N-1]; i=1; }
    }

    mt->state[0] = 0x80000000U; /* MSB is 1; assuring non-zero initial array */
}

static void
next_state(struct MT *mt)
{
    unsigned int *p = mt->state;
    int j;

    /* if init_genrand() has not been called, */
    /* a default initial seed is used         */
    if (!genrand_initialized(mt)) init_genrand(mt, 5489U);

    mt->left = N;
    mt->next = mt->state;

    for (j=N-M+1; --j; p++)
        *p = p[M] ^ TWIST(p[0], p[1]);

    for (j=M; --j; p++)
        *p = p[M-N] ^ TWIST(p[0], p[1]);

    *p = p[M-N] ^ TWIST(p[0], mt->state[0]);
}

/* generates a random number on [0,0xffffffff]-interval */
static unsigned int
genrand_int32(struct MT *mt)
{
    unsigned int y;

    if (--mt->left <= 0) next_state(mt);
    y = *mt->next++;

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

    return y;
}

/* generates a random number on [0,1) with 53-bit resolution*/
static double
genrand_real(struct MT *mt)
{
    unsigned int a = genrand_int32(mt)>>5, b = genrand_int32(mt)>>6;
    return(a*67108864.0+b)*(1.0/9007199254740992.0);
}

/* generates a random number on [0,1] with 53-bit resolution*/
// TODO
#define genrand_real2 genrand_real

/* These real versions are due to Isaku Wada, 2002/01/09 added */

#undef N
#undef M