libgfortran/intrinsics/rand.c

   1 /* Implementation of the IRAND, RAND, and SRAND intrinsics.
   2    Copyright (C) 2004, 2005 Free Software Foundation, Inc.
   3    Contributed by Steven G. Kargl <kargls@comcast.net>.
   4
   5 This file is part of the GNU Fortran 95 runtime library (libgfortran).
   6
   7 Libgfortran is free software; you can redistribute it and/or
   8 modify it under the terms of the GNU General Public
   9 License as published by the Free Software Foundation; either
  10 version 2 of the License, or (at your option) any later version.
  11
  12 In addition to the permissions in the GNU General Public License, the
  13 Free Software Foundation gives you unlimited permission to link the
  14 compiled version of this file into combinations with other programs,
  15 and to distribute those combinations without any restriction coming
  16 from the use of this file.  (The General Public License restrictions
  17 do apply in other respects; for example, they cover modification of
  18 the file, and distribution when not linked into a combine
  19 executable.)
  20
  21 Libgfortran is distributed in the hope that it will be useful,
  22 but WITHOUT ANY WARRANTY; without even the implied warranty of
  23 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  24 GNU General Public License for more details.
  25
  26 You should have received a copy of the GNU General Public
  27 License along with libgfortran; see the file COPYING.  If not,
  28 write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  29 Boston, MA 02110-1301, USA.  */
  30
  31 /* Simple multiplicative congruent algorithm.
  32    The period of this generator is approximately 2^31-1, which means that
  33    it should not be used for anything serious.  The implementation here
  34    is based of an algorithm from  S.K. Park and K.W. Miller, Comm. ACM,
  35    31, 1192-1201 (1988).  It is also provided solely for compatibility
  36    with G77.  */
  37
  38 #include "config.h"
  39 #include "libgfortran.h"
  40 #include <gthr.h>
  41
  42 #define GFC_RAND_A      16807
  43 #define GFC_RAND_M      2147483647
  44 #define GFC_RAND_M1     (GFC_RAND_M - 1)
  45
  46 static GFC_UINTEGER_8 rand_seed = 1;
  47 #ifdef __GTHREAD_MUTEX_INIT
  48 static __gthread_mutex_t rand_seed_lock = __GTHREAD_MUTEX_INIT;
  49 #else
  50 static __gthread_mutex_t rand_seed_lock;
  51 #endif
  52
  53
  54 /* Set the seed of the irand generator.  Note 0 is a bad seed.  */
  55
  56 static void
  57 srand_internal (GFC_INTEGER_8 i)
  58 {
  59   rand_seed = i ? i : 123459876;
  60 }
  61
  62 extern void PREFIX(srand) (GFC_INTEGER_4 *i);
  63 export_proto_np(PREFIX(srand));
  64
  65 void
  66 PREFIX(srand) (GFC_INTEGER_4 *i)
  67 {
  68   __gthread_mutex_lock (&rand_seed_lock);
  69   srand_internal (*i);
  70   __gthread_mutex_unlock (&rand_seed_lock);
  71 }
  72
  73 /* Return an INTEGER in the range [1,GFC_RAND_M-1].  */
  74
  75 extern GFC_INTEGER_4 irand (GFC_INTEGER_4 *);
  76 iexport_proto(irand);
  77
  78 GFC_INTEGER_4
  79 irand (GFC_INTEGER_4 *i)
  80 {
  81   GFC_INTEGER_4 j;
  82   if (i)
  83     j = *i;
  84   else
  85     j = 0;
  86
  87   __gthread_mutex_lock (&rand_seed_lock);
  88
  89   switch (j)
  90   {
  91     /* Return the next RN. */
  92     case 0:
  93       break;
  94
  95     /* Reset the RN sequence to system-dependent sequence and return the
  96        first value.  */
  97     case 1:
  98       srand_internal (0);
  99       break;
 100
 101     /* Seed the RN sequence with j and return the first value.  */
 102     default:
 103       srand_internal (j);
 104       break;
 105    }
 106
 107    rand_seed = GFC_RAND_A * rand_seed % GFC_RAND_M;
 108    j = (GFC_INTEGER_4) rand_seed;
 109
 110   __gthread_mutex_unlock (&rand_seed_lock);
 111
 112    return j;
 113 }
 114 iexport(irand);
 115
 116
 117 /*  Return a random REAL in the range [0,1).  */
 118
 119 extern GFC_REAL_4 PREFIX(rand) (GFC_INTEGER_4 *i);
 120 export_proto_np(PREFIX(rand));
 121
 122 GFC_REAL_4
 123 PREFIX(rand) (GFC_INTEGER_4 *i)
 124 {
 125   GFC_UINTEGER_4 mask;
 126 #if GFC_REAL_4_RADIX == 2
 127   mask = ~ (GFC_UINTEGER_4) 0u << (32 - GFC_REAL_4_DIGITS + 1);
 128 #elif GFC_REAL_4_RADIX == 16
 129   mask = ~ (GFC_UINTEGER_4) 0u << ((8 - GFC_REAL_4_DIGITS) * 4 + 1);
 130 #else
 131 #error "GFC_REAL_4_RADIX has unknown value"
 132 #endif
 133   return ((GFC_UINTEGER_4) (irand(i) -1) & mask) * (GFC_REAL_4) 0x1.p-31f;
 134 }
 135
 136 #ifndef __GTHREAD_MUTEX_INIT
 137 static void __attribute__((constructor))
 138 init (void)
 139 {
 140   __GTHREAD_MUTEX_INIT_FUNCTION (&rand_seed_lock);
 141 }
 142 #endif