1 /* GLIB - Library of useful routines for C programming
2 * Copyright (C) 1995-1997 Peter Mattis, Spencer Kimball and Josh MacDonald
4 * This library is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU Lesser General Public
6 * License as published by the Free Software Foundation; either
7 * version 2 of the License, or (at your option) any later version.
9 * This library is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * Lesser General Public License for more details.
14 * You should have received a copy of the GNU Lesser General Public
15 * License along with this library; if not, write to the
16 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
17 * Boston, MA 02111-1307, USA.
20 /* Originally developed and coded by Makoto Matsumoto and Takuji
21 * Nishimura. Please mail <matumoto@math.keio.ac.jp>, if you're using
22 * code from this file in your own programs or libraries.
23 * Further information on the Mersenne Twister can be found at
24 * http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html
25 * This code was adapted to glib by Sebastian Wilhelmi.
29 * Modified by the GLib Team and others 1997-2000. See the AUTHORS
30 * file for a list of people on the GLib Team. See the ChangeLog
31 * files for a list of changes. These files are distributed with
32 * GLib at ftp://ftp.gtk.org/pub/gtk/.
45 #include <sys/types.h>
51 #include "gthreadprivate.h"
54 #include <process.h> /* For getpid() */
58 * SECTION: random_numbers
59 * @title: Random Numbers
60 * @short_description: pseudo-random number generator
62 * The following functions allow you to use a portable, fast and good
63 * pseudo-random number generator (PRNG). It uses the Mersenne Twister
64 * PRNG, which was originally developed by Makoto Matsumoto and Takuji
65 * Nishimura. Further information can be found at
66 * <ulink url="http://www.math.keio.ac.jp/~matumoto/emt.html">
67 * www.math.keio.ac.jp/~matumoto/emt.html</ulink>.
69 * If you just need a random number, you simply call the
70 * <function>g_random_*</function> functions, which will create a
71 * globally used #GRand and use the according
72 * <function>g_rand_*</function> functions internally. Whenever you
73 * need a stream of reproducible random numbers, you better create a
74 * #GRand yourself and use the <function>g_rand_*</function> functions
75 * directly, which will also be slightly faster. Initializing a #GRand
76 * with a certain seed will produce exactly the same series of random
77 * numbers on all platforms. This can thus be used as a seed for e.g.
80 * The <function>g_rand*_range</function> functions will return high
81 * quality equally distributed random numbers, whereas for example the
82 * <literal>(g_random_int()%max)</literal> approach often
83 * doesn't yield equally distributed numbers.
85 * GLib changed the seeding algorithm for the pseudo-random number
86 * generator Mersenne Twister, as used by
87 * <structname>GRand</structname> and <structname>GRandom</structname>.
88 * This was necessary, because some seeds would yield very bad
89 * pseudo-random streams. Also the pseudo-random integers generated by
90 * <function>g_rand*_int_range()</function> will have a slightly better
91 * equal distribution with the new version of GLib.
93 * The original seeding and generation algorithms, as found in GLib
94 * 2.0.x, can be used instead of the new ones by setting the
95 * environment variable <envar>G_RANDOM_VERSION</envar> to the value of
96 * '2.0'. Use the GLib-2.0 algorithms only if you have sequences of
97 * numbers generated with Glib-2.0 that you need to reproduce exactly.
103 * The #GRand struct is an opaque data structure. It should only be
104 * accessed through the <function>g_rand_*</function> functions.
107 G_LOCK_DEFINE_STATIC (global_random);
108 static GRand* global_random = NULL;
110 /* Period parameters */
113 #define MATRIX_A 0x9908b0df /* constant vector a */
114 #define UPPER_MASK 0x80000000 /* most significant w-r bits */
115 #define LOWER_MASK 0x7fffffff /* least significant r bits */
117 /* Tempering parameters */
118 #define TEMPERING_MASK_B 0x9d2c5680
119 #define TEMPERING_MASK_C 0xefc60000
120 #define TEMPERING_SHIFT_U(y) (y >> 11)
121 #define TEMPERING_SHIFT_S(y) (y << 7)
122 #define TEMPERING_SHIFT_T(y) (y << 15)
123 #define TEMPERING_SHIFT_L(y) (y >> 18)
126 get_random_version (void)
128 static gboolean initialized = FALSE;
129 static guint random_version;
133 const gchar *version_string = g_getenv ("G_RANDOM_VERSION");
134 if (!version_string || version_string[0] == '\000' ||
135 strcmp (version_string, "2.2") == 0)
137 else if (strcmp (version_string, "2.0") == 0)
141 g_warning ("Unknown G_RANDOM_VERSION \"%s\". Using version 2.2.",
148 return random_version;
151 /* This is called from g_thread_init(). It's used to
152 * initialize some static data in a threadsafe way.
155 _g_rand_thread_init (void)
157 (void)get_random_version ();
162 guint32 mt[N]; /* the array for the state vector */
167 * g_rand_new_with_seed:
168 * @seed: a value to initialize the random number generator.
170 * Creates a new random number generator initialized with @seed.
172 * Return value: the new #GRand.
175 g_rand_new_with_seed (guint32 seed)
177 GRand *rand = g_new0 (GRand, 1);
178 g_rand_set_seed (rand, seed);
183 * g_rand_new_with_seed_array:
184 * @seed: an array of seeds to initialize the random number generator.
185 * @seed_length: an array of seeds to initialize the random number generator.
187 * Creates a new random number generator initialized with @seed.
189 * Return value: the new #GRand.
194 g_rand_new_with_seed_array (const guint32 *seed, guint seed_length)
196 GRand *rand = g_new0 (GRand, 1);
197 g_rand_set_seed_array (rand, seed, seed_length);
204 * Creates a new random number generator initialized with a seed taken
205 * either from <filename>/dev/urandom</filename> (if existing) or from
206 * the current time (as a fallback).
208 * Return value: the new #GRand.
216 static gboolean dev_urandom_exists = TRUE;
218 if (dev_urandom_exists)
225 dev_urandom = fopen("/dev/urandom", "rb");
227 while G_UNLIKELY (errno == EINTR);
233 setvbuf (dev_urandom, NULL, _IONBF, 0);
237 r = fread (seed, sizeof (seed), 1, dev_urandom);
239 while G_UNLIKELY (errno == EINTR);
242 dev_urandom_exists = FALSE;
244 fclose (dev_urandom);
247 dev_urandom_exists = FALSE;
250 static gboolean dev_urandom_exists = FALSE;
253 if (!dev_urandom_exists)
255 g_get_current_time (&now);
256 seed[0] = now.tv_sec;
257 seed[1] = now.tv_usec;
260 seed[3] = getppid ();
266 return g_rand_new_with_seed_array (seed, 4);
273 * Frees the memory allocated for the #GRand.
276 g_rand_free (GRand* rand)
278 g_return_if_fail (rand != NULL);
287 * Copies a #GRand into a new one with the same exact state as before.
288 * This way you can take a snapshot of the random number generator for
291 * Return value: the new #GRand.
296 g_rand_copy (GRand* rand)
300 g_return_val_if_fail (rand != NULL, NULL);
302 new_rand = g_new0 (GRand, 1);
303 memcpy (new_rand, rand, sizeof (GRand));
311 * @seed: a value to reinitialize the random number generator.
313 * Sets the seed for the random number generator #GRand to @seed.
316 g_rand_set_seed (GRand* rand, guint32 seed)
318 g_return_if_fail (rand != NULL);
320 switch (get_random_version ())
323 /* setting initial seeds to mt[N] using */
324 /* the generator Line 25 of Table 1 in */
325 /* [KNUTH 1981, The Art of Computer Programming */
326 /* Vol. 2 (2nd Ed.), pp102] */
328 if (seed == 0) /* This would make the PRNG procude only zeros */
329 seed = 0x6b842128; /* Just set it to another number */
332 for (rand->mti=1; rand->mti<N; rand->mti++)
333 rand->mt[rand->mti] = (69069 * rand->mt[rand->mti-1]);
337 /* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
338 /* In the previous version (see above), MSBs of the */
339 /* seed affect only MSBs of the array mt[]. */
342 for (rand->mti=1; rand->mti<N; rand->mti++)
343 rand->mt[rand->mti] = 1812433253UL *
344 (rand->mt[rand->mti-1] ^ (rand->mt[rand->mti-1] >> 30)) + rand->mti;
347 g_assert_not_reached ();
352 * g_rand_set_seed_array:
354 * @seed: array to initialize with
355 * @seed_length: length of array
357 * Initializes the random number generator by an array of
358 * longs. Array can be of arbitrary size, though only the
359 * first 624 values are taken. This function is useful
360 * if you have many low entropy seeds, or if you require more then
361 * 32bits of actual entropy for your application.
366 g_rand_set_seed_array (GRand* rand, const guint32 *seed, guint seed_length)
370 g_return_if_fail (rand != NULL);
371 g_return_if_fail (seed_length >= 1);
373 g_rand_set_seed (rand, 19650218UL);
376 k = (N>seed_length ? N : seed_length);
379 rand->mt[i] = (rand->mt[i] ^
380 ((rand->mt[i-1] ^ (rand->mt[i-1] >> 30)) * 1664525UL))
381 + seed[j] + j; /* non linear */
382 rand->mt[i] &= 0xffffffffUL; /* for WORDSIZE > 32 machines */
386 rand->mt[0] = rand->mt[N-1];
394 rand->mt[i] = (rand->mt[i] ^
395 ((rand->mt[i-1] ^ (rand->mt[i-1] >> 30)) * 1566083941UL))
396 - i; /* non linear */
397 rand->mt[i] &= 0xffffffffUL; /* for WORDSIZE > 32 machines */
401 rand->mt[0] = rand->mt[N-1];
406 rand->mt[0] = 0x80000000UL; /* MSB is 1; assuring non-zero initial array */
412 * @Returns: a random #gboolean.
414 * Returns a random #gboolean from @rand_. This corresponds to a
415 * unbiased coin toss.
421 * Returns the next random #guint32 from @rand_ equally distributed over
422 * the range [0..2^32-1].
424 * Return value: A random number.
427 g_rand_int (GRand* rand)
430 static const guint32 mag01[2]={0x0, MATRIX_A};
431 /* mag01[x] = x * MATRIX_A for x=0,1 */
433 g_return_val_if_fail (rand != NULL, 0);
435 if (rand->mti >= N) { /* generate N words at one time */
438 for (kk=0;kk<N-M;kk++) {
439 y = (rand->mt[kk]&UPPER_MASK)|(rand->mt[kk+1]&LOWER_MASK);
440 rand->mt[kk] = rand->mt[kk+M] ^ (y >> 1) ^ mag01[y & 0x1];
443 y = (rand->mt[kk]&UPPER_MASK)|(rand->mt[kk+1]&LOWER_MASK);
444 rand->mt[kk] = rand->mt[kk+(M-N)] ^ (y >> 1) ^ mag01[y & 0x1];
446 y = (rand->mt[N-1]&UPPER_MASK)|(rand->mt[0]&LOWER_MASK);
447 rand->mt[N-1] = rand->mt[M-1] ^ (y >> 1) ^ mag01[y & 0x1];
452 y = rand->mt[rand->mti++];
453 y ^= TEMPERING_SHIFT_U(y);
454 y ^= TEMPERING_SHIFT_S(y) & TEMPERING_MASK_B;
455 y ^= TEMPERING_SHIFT_T(y) & TEMPERING_MASK_C;
456 y ^= TEMPERING_SHIFT_L(y);
461 /* transform [0..2^32] -> [0..1] */
462 #define G_RAND_DOUBLE_TRANSFORM 2.3283064365386962890625e-10
467 * @begin: lower closed bound of the interval.
468 * @end: upper open bound of the interval.
470 * Returns the next random #gint32 from @rand_ equally distributed over
471 * the range [@begin..@end-1].
473 * Return value: A random number.
476 g_rand_int_range (GRand* rand, gint32 begin, gint32 end)
478 guint32 dist = end - begin;
481 g_return_val_if_fail (rand != NULL, begin);
482 g_return_val_if_fail (end > begin, begin);
484 switch (get_random_version ())
487 if (dist <= 0x10000L) /* 2^16 */
489 /* This method, which only calls g_rand_int once is only good
490 * for (end - begin) <= 2^16, because we only have 32 bits set
491 * from the one call to g_rand_int (). */
493 /* we are using (trans + trans * trans), because g_rand_int only
494 * covers [0..2^32-1] and thus g_rand_int * trans only covers
495 * [0..1-2^-32], but the biggest double < 1 is 1-2^-52.
498 gdouble double_rand = g_rand_int (rand) *
499 (G_RAND_DOUBLE_TRANSFORM +
500 G_RAND_DOUBLE_TRANSFORM * G_RAND_DOUBLE_TRANSFORM);
502 random = (gint32) (double_rand * dist);
506 /* Now we use g_rand_double_range (), which will set 52 bits for
507 us, so that it is safe to round and still get a decent
509 random = (gint32) g_rand_double_range (rand, 0, dist);
517 /* maxvalue is set to the predecessor of the greatest
518 * multiple of dist less or equal 2^32. */
520 if (dist <= 0x80000000u) /* 2^31 */
522 /* maxvalue = 2^32 - 1 - (2^32 % dist) */
523 guint32 leftover = (0x80000000u % dist) * 2;
524 if (leftover >= dist) leftover -= dist;
525 maxvalue = 0xffffffffu - leftover;
531 random = g_rand_int (rand);
532 while (random > maxvalue);
538 random = 0; /* Quiet GCC */
539 g_assert_not_reached ();
542 return begin + random;
549 * Returns the next random #gdouble from @rand_ equally distributed over
552 * Return value: A random number.
555 g_rand_double (GRand* rand)
557 /* We set all 52 bits after the point for this, not only the first
558 32. Thats why we need two calls to g_rand_int */
559 gdouble retval = g_rand_int (rand) * G_RAND_DOUBLE_TRANSFORM;
560 retval = (retval + g_rand_int (rand)) * G_RAND_DOUBLE_TRANSFORM;
562 /* The following might happen due to very bad rounding luck, but
563 * actually this should be more than rare, we just try again then */
565 return g_rand_double (rand);
571 * g_rand_double_range:
573 * @begin: lower closed bound of the interval.
574 * @end: upper open bound of the interval.
576 * Returns the next random #gdouble from @rand_ equally distributed over
577 * the range [@begin..@end).
579 * Return value: A random number.
582 g_rand_double_range (GRand* rand, gdouble begin, gdouble end)
584 return g_rand_double (rand) * (end - begin) + begin;
589 * @Returns: a random #gboolean.
591 * Returns a random #gboolean. This corresponds to a unbiased coin toss.
596 * Return a random #guint32 equally distributed over the range
599 * Return value: A random number.
605 G_LOCK (global_random);
607 global_random = g_rand_new ();
609 result = g_rand_int (global_random);
610 G_UNLOCK (global_random);
615 * g_random_int_range:
616 * @begin: lower closed bound of the interval.
617 * @end: upper open bound of the interval.
619 * Returns a random #gint32 equally distributed over the range
622 * Return value: A random number.
625 g_random_int_range (gint32 begin, gint32 end)
628 G_LOCK (global_random);
630 global_random = g_rand_new ();
632 result = g_rand_int_range (global_random, begin, end);
633 G_UNLOCK (global_random);
640 * Returns a random #gdouble equally distributed over the range [0..1).
642 * Return value: A random number.
645 g_random_double (void)
648 G_LOCK (global_random);
650 global_random = g_rand_new ();
652 result = g_rand_double (global_random);
653 G_UNLOCK (global_random);
658 * g_random_double_range:
659 * @begin: lower closed bound of the interval.
660 * @end: upper open bound of the interval.
662 * Returns a random #gdouble equally distributed over the range [@begin..@end).
664 * Return value: A random number.
667 g_random_double_range (gdouble begin, gdouble end)
670 G_LOCK (global_random);
672 global_random = g_rand_new ();
674 result = g_rand_double_range (global_random, begin, end);
675 G_UNLOCK (global_random);
681 * @seed: a value to reinitialize the global random number generator.
683 * Sets the seed for the global random number generator, which is used
684 * by the <function>g_random_*</function> functions, to @seed.
687 g_random_set_seed (guint32 seed)
689 G_LOCK (global_random);
691 global_random = g_rand_new_with_seed (seed);
693 g_rand_set_seed (global_random, seed);
694 G_UNLOCK (global_random);