libgfortran/intrinsics/rand.c

   1 /* Implementation of the IRAND, RAND, and SRAND intrinsics.
   2    Copyright (C) 2004 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., 59 Temple Place - Suite 330,
  29 Boston, MA 02111-1307, 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
  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
  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   srand_internal (*i);
  63 }
  64
  65 /* Return an INTEGER in the range [1,GFC_RAND_M-1].  */
  66
  67 extern GFC_INTEGER_4 irand (GFC_INTEGER_4 *);
  68 iexport_proto(irand);
  69
  70 GFC_INTEGER_4
  71 irand (GFC_INTEGER_4 *i)
  72 {
  73   GFC_INTEGER_4 j;
  74   if (i)
  75     j = *i;
  76   else
  77     j = 0;
  78
  79   switch (j)
  80   {
  81     /* Return the next RN. */
  82     case 0:
  83       break;
  84
  85     /* Reset the RN sequence to system-dependent sequence and return the
  86        first value.  */
  87     case 1:
  88       srand_internal (0);
  89       break;
  90
  91     /* Seed the RN sequence with j and return the first value.  */
  92     default:
  93       srand_internal (j);
  94       break;
  95    }
  96
  97    rand_seed = GFC_RAND_A * rand_seed % GFC_RAND_M;
  98
  99    return (GFC_INTEGER_4) rand_seed;
 100 }
 101 iexport(irand);
 102
 103
 104 /*  Return a random REAL in the range [0,1).  */
 105
 106 extern GFC_REAL_4 PREFIX(rand) (GFC_INTEGER_4 *i);
 107 export_proto_np(PREFIX(rand));
 108
 109 GFC_REAL_4
 110 PREFIX(rand) (GFC_INTEGER_4 *i)
 111 {
 112   return normalize_r4_i4 (irand (i) - 1, GFC_RAND_M1 - 1);
 113 }