libgfortran/intrinsics/rand.c

   1 /* Implementation of the IRAND, RAND, and SRAND intrinsics.
   2    Copyright (C) 2004-2024 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 3 of the License, or (at your option) any later version.
  11
  12 Libgfortran 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 General Public License for more details.
  16
  17 Under Section 7 of GPL version 3, you are granted additional
  18 permissions described in the GCC Runtime Library Exception, version
  19 3.1, as published by the Free Software Foundation.
  20
  21 You should have received a copy of the GNU General Public License and
  22 a copy of the GCC Runtime Library Exception along with this program;
  23 see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  24 <http://www.gnu.org/licenses/>.  */
  25
  26 /* Simple multiplicative congruent algorithm.
  27    The period of this generator is approximately 2^31-1, which means that
  28    it should not be used for anything serious.  The implementation here
  29    is based of an algorithm from  S.K. Park and K.W. Miller, Comm. ACM,
  30    31, 1192-1201 (1988).  It is also provided solely for compatibility
  31    with G77.  */
  32
  33 #include "libgfortran.h"
  34 #include <gthr.h>
  35
  36 #define GFC_RAND_A      16807
  37 #define GFC_RAND_M      2147483647
  38 #define GFC_RAND_M1     (GFC_RAND_M - 1)
  39
  40 static GFC_UINTEGER_8 rand_seed = 1;
  41 #ifdef __GTHREAD_MUTEX_INIT
  42 static __gthread_mutex_t rand_seed_lock = __GTHREAD_MUTEX_INIT;
  43 #else
  44 static __gthread_mutex_t rand_seed_lock;
  45 #endif
  46
  47
  48 /* Set the seed of the irand generator.  Note 0 is a bad seed.  */
  49
  50 static void
  51 srand_internal (GFC_INTEGER_8 i)
  52 {
  53   rand_seed = i ? i : 123459876;
  54 }
  55
  56 extern void PREFIX(srand) (GFC_INTEGER_4 *i);
  57 export_proto_np(PREFIX(srand));
  58
  59 void
  60 PREFIX(srand) (GFC_INTEGER_4 *i)
  61 {
  62   __gthread_mutex_lock (&rand_seed_lock);
  63   srand_internal (*i);
  64   __gthread_mutex_unlock (&rand_seed_lock);
  65 }
  66
  67 /* Return an INTEGER in the range [1,GFC_RAND_M-1].  */
  68
  69 extern GFC_INTEGER_4 irand (GFC_INTEGER_4 *);
  70 iexport_proto(irand);
  71
  72 GFC_INTEGER_4
  73 irand (GFC_INTEGER_4 *i)
  74 {
  75   GFC_INTEGER_4 j;
  76   if (i)
  77     j = *i;
  78   else
  79     j = 0;
  80
  81   __gthread_mutex_lock (&rand_seed_lock);
  82
  83   switch (j)
  84   {
  85     /* Return the next RN. */
  86     case 0:
  87       break;
  88
  89     /* Reset the RN sequence to system-dependent sequence and return the
  90        first value.  */
  91     case 1:
  92       srand_internal (0);
  93       break;
  94
  95     /* Seed the RN sequence with j and return the first value.  */
  96     default:
  97       srand_internal (j);
  98       break;
  99    }
 100
 101    rand_seed = GFC_RAND_A * rand_seed % GFC_RAND_M;
 102    j = (GFC_INTEGER_4) rand_seed;
 103
 104   __gthread_mutex_unlock (&rand_seed_lock);
 105
 106    return j;
 107 }
 108 iexport(irand);
 109
 110
 111 /*  Return a random REAL in the range [0,1).  */
 112
 113 extern GFC_REAL_4 PREFIX(rand) (GFC_INTEGER_4 *i);
 114 export_proto_np(PREFIX(rand));
 115
 116 GFC_REAL_4
 117 PREFIX(rand) (GFC_INTEGER_4 *i)
 118 {
 119   GFC_UINTEGER_4 mask;
 120 #if GFC_REAL_4_RADIX == 2
 121   mask = ~ (GFC_UINTEGER_4) 0u << (32 - GFC_REAL_4_DIGITS + 1);
 122 #elif GFC_REAL_4_RADIX == 16
 123   mask = ~ (GFC_UINTEGER_4) 0u << ((8 - GFC_REAL_4_DIGITS) * 4 + 1);
 124 #else
 125 #error "GFC_REAL_4_RADIX has unknown value"
 126 #endif
 127   return ((GFC_UINTEGER_4) (irand(i) -1) & mask) * (GFC_REAL_4) 0x1.p-31f;
 128 }
 129
 130 #ifndef __GTHREAD_MUTEX_INIT
 131 static void __attribute__((constructor))
 132 init (void)
 133 {
 134   __GTHREAD_MUTEX_INIT_FUNCTION (&rand_seed_lock);
 135 }
 136 #endif