src/misc/rand.c

   1 /*****************************************************************************
   2  * rand.c : non-predictible random bytes generator
   3  *****************************************************************************
   4  * Copyright © 2007 Rémi Denis-Courmont
   5  * $Id$
   6  *
   7  * This program is free software; you can redistribute it and/or modify it
   8  * under the terms of the GNU Lesser General Public License as published by
   9  * the Free Software Foundation; either version 2.1 of the License, or
  10  * (at your option) any later version.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  15  * GNU Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public License
  18  * along with this program; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
  20  *****************************************************************************/
  21
  22 #ifdef HAVE_CONFIG_H
  23 # include "config.h"
  24 #endif
  25
  26 #include <vlc_common.h>
  27 #include <vlc_rand.h>
  28
  29 static struct
  30 {
  31     bool           init;
  32     unsigned short subi[3];
  33     vlc_mutex_t    lock;
  34 } rand48 = { false, { 0, 0, 0, }, VLC_STATIC_MUTEX, };
  35
  36 static void init_rand48 (void)
  37 {
  38     if (!rand48.init)
  39     {
  40         vlc_rand_bytes (rand48.subi, sizeof (rand48.subi));
  41         rand48.init = true;
  42 #if 0 // short would be more than 16-bits ?
  43         for (unsigned i = 0; i < 3; i++)
  44             subi[i] &= 0xffff;
  45 #endif
  46     }
  47 }
  48
  49 /**
  50  * PRNG uniformly distributed between 0.0 and 1.0 with 48-bits precision.
  51  *
  52  * @note Contrary to POSIX drand48(), this function is thread-safe.
  53  * @warning Series generated by this function are not reproducible.
  54  * Use erand48() if you need reproducible series.
  55  *
  56  * @return a double value within [0.0, 1.0] inclusive
  57  */
  58 double vlc_drand48 (void)
  59 {
  60     double ret;
  61
  62     vlc_mutex_lock (&rand48.lock);
  63     init_rand48 ();
  64     ret = erand48 (rand48.subi);
  65     vlc_mutex_unlock (&rand48.lock);
  66     return ret;
  67 }
  68
  69 /**
  70  * PRNG uniformly distributed between 0 and 2^32 - 1.
  71  *
  72  * @note Contrary to POSIX lrand48(), this function is thread-safe.
  73  * @warning Series generated by this function are not reproducible.
  74  * Use nrand48() if you need reproducible series.
  75  *
  76  * @return an integral value within [0.0, 2^32-1] inclusive
  77  */
  78 long vlc_lrand48 (void)
  79 {
  80     long ret;
  81
  82     vlc_mutex_lock (&rand48.lock);
  83     init_rand48 ();
  84     ret = nrand48 (rand48.subi);
  85     vlc_mutex_unlock (&rand48.lock);
  86     return ret;
  87 }
  88
  89 /**
  90  * PRNG uniformly distributed between -2^32 and 2^32 - 1.
  91  *
  92  * @note Contrary to POSIX mrand48(), this function is thread-safe.
  93  * @warning Series generated by this function are not reproducible.
  94  * Use jrand48() if you need reproducible series.
  95  *
  96  * @return an integral value within [-2^32, 2^32-1] inclusive
  97  */
  98 long vlc_mrand48 (void)
  99 {
 100     long ret;
 101
 102     vlc_mutex_lock (&rand48.lock);
 103     init_rand48 ();
 104     ret = jrand48 (rand48.subi);
 105     vlc_mutex_unlock (&rand48.lock);
 106     return ret;
 107 }