path: root/random.c

/* libnul - another utility library */

/* Based on grand.c from GLib. GLib copyright:
 *
 * Copyright (C) 1995-1997  Peter Mattis, Spencer Kimball and Josh MacDonald
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

/* Originally developed and coded by Makoto Matsumoto and Takuji
 * Nishimura.  Please mail <matumoto@math.keio.ac.jp>, if you're using
 * code from this file in your own programs or libraries.
 * Further information on the Mersenne Twister can be found at
 * http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html
 * This code was adapted to glib by Sebastian Wilhelmi.
 */

/*
 * Modified by the GLib Team and others 1997-2000.  See the AUTHORS
 * file for a list of people on the GLib Team.  See the ChangeLog
 * files for a list of changes.  These files are distributed with
 * GLib at ftp://ftp.gtk.org/pub/gtk/.
 */

/*
 * MT safe
 */

#include "config.h"
#include "libnul.h"

#include <math.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

typedef struct _rand_t rand_t;

G_LOCK_DEFINE_STATIC (global_random);
static rand_t* global_random = NULL;

/* 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)

struct _rand_t
{
    uint32_t mt[N]; /* the array for the state vector  */
    guint mti;
};

/**
 * nul_rand_set_seed:
 * @rand_: a #rand_t.
 * @seed: a value to reinitialize the random number generator.
 *
 * Sets the seed for the random number generator #rand_t to @seed.
 **/
static void
nul_rand_set_seed (rand_t* rand, uint32_t seed)
{
    g_return_if_fail (rand != NULL);

    /* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
    /* In the previous version (see above), MSBs of the    */
    /* seed affect only MSBs of the array mt[].            */

    rand->mt[0]= seed;
    for (rand->mti=1; rand->mti<N; rand->mti++)
    {
	rand->mt[rand->mti] = 1812433253UL *
	    (rand->mt[rand->mti-1] ^ (rand->mt[rand->mti-1] >> 30)) + rand->mti;
    }
}

/**
 * nul_rand_set_seed_array:
 * @rand_: a #rand_t.
 * @seed: array to initialize with
 * @seed_length: length of array
 *
 * Initializes the random number generator by an array of
 * longs.  Array can be of arbitrary size, though only the
 * first 624 values are taken.  This function is useful
 * if you have many low entropy seeds, or if you require more then
 * 32bits of actual entropy for your application.
 *
 * Since: 2.4
 **/
static void
nul_rand_set_seed_array (rand_t* rand, const uint32_t *seed, guint seed_length)
{
    int i, j, k;

    g_return_if_fail (rand != NULL);
    g_return_if_fail (seed_length >= 1);

    nul_rand_set_seed (rand, 19650218UL);

    i=1; j=0;
    k = (N>seed_length ? N : seed_length);
    for (; k; k--)
    {
	rand->mt[i] = (rand->mt[i] ^
		       ((rand->mt[i-1] ^ (rand->mt[i-1] >> 30)) * 1664525UL))
	    + seed[j] + j; /* non linear */
	rand->mt[i] &= 0xffffffffUL; /* for WORDSIZE > 32 machines */
	i++; j++;
	if (i>=N)
        {
	    rand->mt[0] = rand->mt[N-1];
	    i=1;
	}
	if (j>=seed_length)
	    j=0;
    }
    for (k=N-1; k; k--)
    {
	rand->mt[i] = (rand->mt[i] ^
		       ((rand->mt[i-1] ^ (rand->mt[i-1] >> 30)) * 1566083941UL))
	    - i; /* non linear */
	rand->mt[i] &= 0xffffffffUL; /* for WORDSIZE > 32 machines */
	i++;
	if (i>=N)
        {
	    rand->mt[0] = rand->mt[N-1];
	    i=1;
	}
    }

    rand->mt[0] = 0x80000000UL; /* MSB is 1; assuring non-zero initial array */
}

/**
 * nul_rand_new_with_seed:
 * @seed: a value to initialize the random number generator.
 *
 * Creates a new random number generator initialized with @seed.
 *
 * Return value: the new #rand_t.
 **/
static rand_t*
nul_rand_new_with_seed (uint32_t seed)
{
    rand_t *rand = g_new0 (rand_t, 1);
    nul_rand_set_seed (rand, seed);
    return rand;
}

/**
 * nul_rand_new_with_seed_array:
 * @seed: an array of seeds to initialize the random number generator.
 * @seed_length: an array of seeds to initialize the random number generator.
 *
 * Creates a new random number generator initialized with @seed.
 *
 * Return value: the new #rand_t.
 *
 * Since: 2.4
 **/
static rand_t*
nul_rand_new_with_seed_array (const uint32_t *seed, guint seed_length)
{
    rand_t *rand = g_new0 (rand_t, 1);

    nul_rand_set_seed_array (rand, seed, seed_length);

    return rand;
}

/**
 * nul_rand_new:
 *
 * Creates a new random number generator initialized with a seed taken
 * either from <filename>/dev/urandom</filename> (if existing) or from
 * the current time (as a fallback).
 *
 * Return value: the new #rand_t.
 **/
static rand_t*
nul_rand_new (void)
{
    uint32_t seed[4];
    GTimeVal now;
#ifdef G_OS_UNIX
    static gboolean dev_urandom_exists = TRUE;

    if (dev_urandom_exists)
    {
	FILE* dev_urandom;

	do
        {
	    errno = 0;
	    dev_urandom = fopen("/dev/urandom", "rb");
	}
	while G_UNLIKELY (errno == EINTR);

	if (dev_urandom)
	{
	    int r;

	    do
	    {
		errno = 0;
		r = fread (seed, sizeof (seed), 1, dev_urandom);
	    }
	    while G_UNLIKELY (errno == EINTR);

	    if (r != 1)
		dev_urandom_exists = FALSE;

	    fclose (dev_urandom);
	}
	else
	    dev_urandom_exists = FALSE;
    }
#else
    static gboolean dev_urandom_exists = FALSE;
#endif

    if (!dev_urandom_exists)
    {
	g_get_current_time (&now);
	seed[0] = now.tv_sec;
	seed[1] = now.tv_usec;
	seed[2] = getpid ();
#ifdef G_OS_UNIX
	seed[3] = getppid ();
#else
	seed[3] = 0;
#endif
    }

    return nul_rand_new_with_seed_array (seed, 4);
}

/**
 * nul_rand_int:
 * @rand_: a #rand_t.
 *
 * Returns the next random #uint32_t from @rand_ equally distributed over
 * the range [0..2^32-1].
 *
 * Return value: A random number.
 **/
static uint32_t
nul_rand_int (rand_t* rand)
{
    uint32_t y;
    static const uint32_t mag01[2]={0x0, MATRIX_A};
    /* mag01[x] = x * MATRIX_A  for x=0,1 */

    g_return_val_if_fail (rand != NULL, 0);

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

	for (kk=0;kk<N-M;kk++) {
	    y = (rand->mt[kk]&UPPER_MASK)|(rand->mt[kk+1]&LOWER_MASK);
	    rand->mt[kk] = rand->mt[kk+M] ^ (y >> 1) ^ mag01[y & 0x1];
	}
	for (;kk<N-1;kk++) {
	    y = (rand->mt[kk]&UPPER_MASK)|(rand->mt[kk+1]&LOWER_MASK);
	    rand->mt[kk] = rand->mt[kk+(M-N)] ^ (y >> 1) ^ mag01[y & 0x1];
	}
	y = (rand->mt[N-1]&UPPER_MASK)|(rand->mt[0]&LOWER_MASK);
	rand->mt[N-1] = rand->mt[M-1] ^ (y >> 1) ^ mag01[y & 0x1];

	rand->mti = 0;
    }

    y = rand->mt[rand->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;
}

/* transform [0..2^32] -> [0..1] */
#define NUL_RAND_DOUBLE_TRANSFORM 2.3283064365386962890625e-10

/**
 * nul_rand_int_range:
 * @rand_: a #rand_t.
 * @begin: lower closed bound of the interval.
 * @end: upper open bound of the interval.
 *
 * Returns the next random #int32_t from @rand_ equally distributed over
 * the range [@begin..@end-1].
 *
 * Return value: A random number.
 **/
static int32_t
nul_rand_int_range (rand_t* rand, int32_t begin, int32_t end)
{
    uint32_t dist = end - begin;
    uint32_t random;

    g_return_val_if_fail (rand != NULL, begin);
    g_return_val_if_fail (end > begin, begin);

    if (dist == 0)
	random = 0;
    else
    {
	/* maxvalue is set to the predecessor of the greatest
	 * multiple of dist less or equal 2^32. */
	uint32_t maxvalue;
	if (dist <= 0x80000000u) /* 2^31 */
	{
	    /* maxvalue = 2^32 - 1 - (2^32 % dist) */
	    uint32_t leftover = (0x80000000u % dist) * 2;
	    if (leftover >= dist) leftover -= dist;
	    maxvalue = 0xffffffffu - leftover;
	}
	else
	    maxvalue = dist - 1;

	do
	    random = nul_rand_int (rand);
	while (random > maxvalue);

	random %= dist;
    }
    return begin + random;
}

/**
 * nul_rand_double:
 * @rand_: a #rand_t.
 *
 * Returns the next random #double from @rand_ equally distributed over
 * the range [0..1).
 *
 * Return value: A random number.
 **/
static double
nul_rand_double (rand_t* rand)
{
    /* We set all 52 bits after the point for this, not only the first
       32. Thats why we need two calls to nul_rand_int */
    double retval = nul_rand_int (rand) * NUL_RAND_DOUBLE_TRANSFORM;
    retval = (retval + nul_rand_int (rand)) * NUL_RAND_DOUBLE_TRANSFORM;

    /* The following might happen due to very bad rounding luck, but
     * actually this should be more than rare, we just try again then */
    if (retval >= 1.0)
	return nul_rand_double (rand);

    return retval;
}

/**
 * nul_rand_double_range:
 * @rand_: a #rand_t.
 * @begin: lower closed bound of the interval.
 * @end: upper open bound of the interval.
 *
 * Returns the next random #double from @rand_ equally distributed over
 * the range [@begin..@end).
 *
 * Return value: A random number.
 **/
static double
nul_rand_double_range (rand_t* rand, double begin, double end)
{
    return nul_rand_double (rand) * (end - begin) + begin;
}

/**
 * nul_random_int:
 *
 * Return a random #uint32_t equally distributed over the range
 * [0..2^32-1].
 *
 * Return value: A random number.
 **/
uint32_t
nul_random_int (void)
{
    uint32_t result;
    G_LOCK (global_random);
    if (!global_random)
	global_random = nul_rand_new ();

    result = nul_rand_int (global_random);
    G_UNLOCK (global_random);
    return result;
}

/**
 * nul_random_int_range:
 * @begin: lower closed bound of the interval.
 * @end: upper open bound of the interval.
 *
 * Returns a random #int32_t equally distributed over the range
 * [@begin..@end-1].
 *
 * Return value: A random number.
 **/
int32_t
nul_random_int_range (int32_t begin, int32_t end)
{
    int32_t result;
    G_LOCK (global_random);
    if (!global_random)
	global_random = nul_rand_new ();

    result = nul_rand_int_range (global_random, begin, end);
    G_UNLOCK (global_random);
    return result;
}

/**
 * nul_random_double:
 *
 * Returns a random #double equally distributed over the range [0..1).
 *
 * Return value: A random number.
 **/
double
nul_random_double (void)
{
    double result;
    G_LOCK (global_random);
    if (!global_random)
	global_random = nul_rand_new ();

    result = nul_rand_double (global_random);
    G_UNLOCK (global_random);
    return result;
}

/**
 * nul_random_double_range:
 * @begin: lower closed bound of the interval.
 * @end: upper open bound of the interval.
 *
 * Returns a random #double equally distributed over the range [@begin..@end).
 *
 * Return value: A random number.
 **/
double
nul_random_double_range (double begin, double end)
{
    double result;
    G_LOCK (global_random);
    if (!global_random)
	global_random = nul_rand_new ();

    result = nul_rand_double_range (global_random, begin, end);
    G_UNLOCK (global_random);
    return result;
}

/**
 * nul_random_set_seed:
 * @seed: a value to reinitialize the global random number generator.
 *
 * Sets the seed for the global random number generator, which is used
 * by the <function>nul_random_*</function> functions, to @seed.
 **/
void
nul_random_set_seed (uint32_t seed)
{
    G_LOCK (global_random);
    if (!global_random)
	global_random = nul_rand_new_with_seed (seed);
    else
	nul_rand_set_seed (global_random, seed);
    G_UNLOCK (global_random);
}


#define __NUL_RAND_C__