libgfortran/intrinsics/rand.c

   1 /* Implementation of the IRAND, RAND, and SRAND intrinsics.
   2    Copyright (C) 2004, 2005, 2007 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 "libgfortran.h"
  39 #include <gthr.h>
  40
  41 #define GFC_RAND_A      16807
  42 #define GFC_RAND_M      2147483647
  43 #define GFC_RAND_M1     (GFC_RAND_M - 1)
  44
  45 static GFC_UINTEGER_8 rand_seed = 1;
  46 #ifdef __GTHREAD_MUTEX_INIT
  47 static __gthread_mutex_t rand_seed_lock = __GTHREAD_MUTEX_INIT;
  48 #else
  49 static __gthread_mutex_t rand_seed_lock;
  50 #endif
  51
  52
  53 /* Set the seed of the irand generator.  Note 0 is a bad seed.  */
  54
  55 static void
  56 srand_internal (GFC_INTEGER_8 i)
  57 {
  58   rand_seed = i ? i : 123459876;
  59 }
  60
  61 extern void PREFIX(srand) (GFC_INTEGER_4 *i);
  62 export_proto_np(PREFIX(srand));
  63
  64 void
  65 PREFIX(srand) (GFC_INTEGER_4 *i)
  66 {
  67   __gthread_mutex_lock (&rand_seed_lock);
  68   srand_internal (*i);
  69   __gthread_mutex_unlock (&rand_seed_lock);
  70 }
  71
  72 /* Return an INTEGER in the range [1,GFC_RAND_M-1].  */
  73
  74 extern GFC_INTEGER_4 irand (GFC_INTEGER_4 *);
  75 iexport_proto(irand);
  76
  77 GFC_INTEGER_4
  78 irand (GFC_INTEGER_4 *i)
  79 {
  80   GFC_INTEGER_4 j;
  81   if (i)
  82     j = *i;
  83   else
  84     j = 0;
  85
  86   __gthread_mutex_lock (&rand_seed_lock);
  87
  88   switch (j)
  89   {
  90     /* Return the next RN. */
  91     case 0:
  92       break;
  93
  94     /* Reset the RN sequence to system-dependent sequence and return the
  95        first value.  */
  96     case 1:
  97       srand_internal (0);
  98       break;
  99
 100     /* Seed the RN sequence with j and return the first value.  */
 101     default:
 102       srand_internal (j);
 103       break;
 104    }
 105
 106    rand_seed = GFC_RAND_A * rand_seed % GFC_RAND_M;
 107    j = (GFC_INTEGER_4) rand_seed;
 108
 109   __gthread_mutex_unlock (&rand_seed_lock);
 110
 111    return j;
 112 }
 113 iexport(irand);
 114
 115
 116 /*  Return a random REAL in the range [0,1).  */
 117
 118 extern GFC_REAL_4 PREFIX(rand) (GFC_INTEGER_4 *i);
 119 export_proto_np(PREFIX(rand));
 120
 121 GFC_REAL_4
 122 PREFIX(rand) (GFC_INTEGER_4 *i)
 123 {
 124   GFC_UINTEGER_4 mask;
 125 #if GFC_REAL_4_RADIX == 2
 126   mask = ~ (GFC_UINTEGER_4) 0u << (32 - GFC_REAL_4_DIGITS + 1);
 127 #elif GFC_REAL_4_RADIX == 16
 128   mask = ~ (GFC_UINTEGER_4) 0u << ((8 - GFC_REAL_4_DIGITS) * 4 + 1);
 129 #else
 130 #error "GFC_REAL_4_RADIX has unknown value"
 131 #endif
 132   return ((GFC_UINTEGER_4) (irand(i) -1) & mask) * (GFC_REAL_4) 0x1.p-31f;
 133 }
 134
 135 #ifndef __GTHREAD_MUTEX_INIT
 136 static void __attribute__((constructor))
 137 init (void)
 138 {
 139   __GTHREAD_MUTEX_INIT_FUNCTION (&rand_seed_lock);
 140 }
 141 #endif