glib/grand.c

/* GLIB - Library of useful routines for C programming
 * 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.keio.ac.jp/~matumoto/emt.html
 * This code was adapted to glib by Sebastian Wilhelmi <wilhelmi@ira.uka.de>.
 */

/*
 * 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 <glib.h>
#include <math.h>
#include <stdio.h>

G_LOCK_DEFINE_STATIC (global_random);
static GRand* 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 _GRand
{
  guint32 mt[N]; /* the array for the state vector  */
  guint mti; 
};

/**
 * g_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 #GRand.
 **/
GRand*
g_rand_new_with_seed (guint32 seed)
{
  GRand *rand = g_new0 (GRand, 1);
  g_rand_set_seed (rand, seed);
  return rand;
}

/**
 * g_rand_new:
 * 
 * Creates a new random number generator initialized with a seed taken
 * either from /dev/urandom (if existing) or from the current time (as
 * a fallback).
 * 
 * Return value: the new #GRand.
 **/
GRand* 
g_rand_new (void)
{
  guint32 seed;
  GTimeVal now;
  static gboolean dev_urandom_exists = TRUE;
  
  if (dev_urandom_exists)
    {
      FILE* dev_urandom = fopen("/dev/urandom", "rb");
      if (dev_urandom)
	{
	  if (fread (&seed, sizeof (seed), 1, dev_urandom) != 1)
	    dev_urandom_exists = FALSE;
	  fclose (dev_urandom);
	}	
      else
	dev_urandom_exists = FALSE;
    }
  if (!dev_urandom_exists)
    {  
      g_get_current_time (&now);
      seed = now.tv_sec ^ now.tv_usec;
    }

  return g_rand_new_with_seed (seed);
}

/**
 * g_rand_free:
 * @rand: a #GRand.
 *
 * Frees the memory allocated for the #GRand.
 **/
void
g_rand_free (GRand* rand)
{
  g_return_if_fail (rand != NULL);

  g_free (rand);
}

/**
 * g_rand_set_seed:
 * @rand: a #GRand.
 * @seed: a value to reinitialize the random number generator.
 *
 * Sets the seed for the random number generator #GRand to @seed.
 **/
void
g_rand_set_seed (GRand* rand, guint32 seed)
{
  g_return_if_fail (rand != NULL);

  /* 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 == 0) /* This would make the PRNG procude only zeros */
    seed = 0x6b842128; /* Just set it to another number */

  rand->mt[0]= seed & 0xffffffff;
  for (rand->mti=1; rand->mti<N; rand->mti++)
    rand->mt[rand->mti] = (69069 * rand->mt[rand->mti-1]) & 0xffffffff;
}

/**
 * g_rand_int:
 * @rand: a #GRand.
 *
 * Return the next random #guint32 from @rand equaly distributed over
 * the range [0..2^32-1].
 *
 * Return value: A random number.
 **/
guint32
g_rand_int (GRand* rand)
{
  guint32 y;
  static const guint32 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 G_RAND_DOUBLE_TRANSFORM 2.3283064365386962890625e-10

/**
 * g_rand_int_range:
 * @rand: a #GRand.
 * @begin: lower closed bound of the interval.
 * @end: upper open bound of the interval.
 *
 * Return the next random #gint32 from @rand equaly distributed over
 * the range [@begin..@end-1].
 *
 * Return value: A random number.
 **/
gint32 
g_rand_int_range (GRand* rand, gint32 begin, gint32 end)
{
  guint32 dist = end - begin;
  guint32 random;

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

  /* All tricks doing modulo calculations do not have a perfect
   * distribution -> We must use the slower way through gdouble for
   * maximal quality. */
   
  if (dist <= 0x10000L) /* 2^16 */
    {
      /* This method, which only calls g_rand_int once is only good
       * for (end - begin) <= 2^16, because we only have 32 bits set
       * from the one call to g_rand_int (). */

      /* we are using (trans + trans * trans), because g_rand_int only
       * covers [0..2^32-1] and thus g_rand_int * trans only covers
       * [0..1-2^-32], but the biggest double < 1 is 1-2^-52. 
       */

      gdouble double_rand = g_rand_int (rand) * 
	(G_RAND_DOUBLE_TRANSFORM +
	 G_RAND_DOUBLE_TRANSFORM * G_RAND_DOUBLE_TRANSFORM);
      
      random = (gint32) (double_rand * dist);
    }
  else
    {
      /* Now we use g_rand_double_range (), which will set 52 bits for
         us, so that it is safe to round and still get a decent
         distribution */
       random = (gint32) g_rand_double_range (rand, 0, dist);
    }
 
  return begin + random;
}

/**
 * g_rand_double:
 * @rand: a #GRand.
 *
 * Return the next random #gdouble from @rand equaly distributed over
 * the range [0..1).
 *
 * Return value: A random number.
 **/
gdouble 
g_rand_double (GRand* rand)
{    
  /* We set all 52 bits after the point for this, not only the first
     32. Thats why we need two calls to g_rand_int */
  gdouble retval = g_rand_int (rand) * G_RAND_DOUBLE_TRANSFORM;
  retval = (retval + g_rand_int (rand)) * G_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 g_rand_double (rand);

  return retval;
}

/**
 * g_rand_double_range:
 * @rand: a #GRand.
 * @begin: lower closed bound of the interval.
 * @end: upper open bound of the interval.
 *
 * Return the next random #gdouble from @rand equaly distributed over
 * the range [@begin..@end).
 *
 * Return value: A random number.
 **/
gdouble 
g_rand_double_range (GRand* rand, gdouble begin, gdouble end)
{
  return g_rand_double (rand) * (end - begin) + begin;
}

/**
 * g_random_int:
 *
 * Return a random #guint32 equaly distributed over the range
 * [0..2^32-1].
 *
 * Return value: A random number.
 **/
guint32
g_random_int (void)
{
  guint32 result;
  G_LOCK (global_random);
  if (!global_random)
    global_random = g_rand_new ();
  
  result = g_rand_int (global_random);
  G_UNLOCK (global_random);
  return result;
}

/**
 * g_random_int_range:
 * @begin: lower closed bound of the interval.
 * @end: upper open bound of the interval.
 *
 * Return a random #gint32 equaly distributed over the range
 * [@begin..@end-1].
 *
 * Return value: A random number.
 **/
gint32 
g_random_int_range (gint32 begin, gint32 end)
{
  gint32 result;
  G_LOCK (global_random);
  if (!global_random)
    global_random = g_rand_new ();
  
  result = g_rand_int_range (global_random, begin, end);
  G_UNLOCK (global_random);
  return result;
}

/**
 * g_random_double:
 *
 * Return a random #gdouble equaly distributed over the range [0..1).
 *
 * Return value: A random number.
 **/
gdouble 
g_random_double (void)
{
  double result;
  G_LOCK (global_random);
  if (!global_random)
    global_random = g_rand_new ();
  
  result = g_rand_double (global_random);
  G_UNLOCK (global_random);
  return result;
}

/**
 * g_random_double_range:
 * @begin: lower closed bound of the interval.
 * @end: upper open bound of the interval.
 *
 * Return a random #gdouble equaly distributed over the range [@begin..@end).
 *
 * Return value: A random number.
 **/
gdouble 
g_random_double_range (gdouble begin, gdouble end)
{
  double result;
  G_LOCK (global_random);
  if (!global_random)
    global_random = g_rand_new ();
 
  result = g_rand_double_range (global_random, begin, end);
  G_UNLOCK (global_random);
  return result;
}

/**
 * g_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 te g_random_* functions, to @seed.
 **/
void
g_random_set_seed (guint32 seed)
{
  G_LOCK (global_random);
  if (!global_random)
    global_random = g_rand_new_with_seed (seed);
  else
    g_rand_set_seed (global_random, seed);
  G_UNLOCK (global_random);
}