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      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 (at) 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
    137