compiler/stdc/rand.c

   1 /*
   2     Copyright © 1995-2016, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     C99 functions rand() and srand().
   6 */
   7
   8 #include "__stdc_intbase.h"
   9
  10 #include <aros/symbolsets.h>
  11
  12 /*****************************************************************************
  13
  14     NAME */
  15 #include <stdlib.h>
  16
  17         int rand (
  18
  19 /*  SYNOPSIS */
  20         void)
  21
  22 /*  FUNCTION
  23         A random number generator.
  24
  25     INPUTS
  26         None.
  27
  28     RESULT
  29         A pseudo-random integer between 0 and RAND_MAX.
  30
  31     NOTES
  32
  33     EXAMPLE
  34
  35     BUGS
  36
  37     SEE ALSO
  38         srand()
  39
  40     INTERNALS
  41
  42 ******************************************************************************/
  43 {
  44     struct StdCIntBase *StdCBase = (struct StdCIntBase *)__aros_getbase_StdCBase();
  45
  46     StdCBase->srand_seed = StdCBase->srand_seed * 1103515245 + 12345;
  47
  48     return ((StdCBase->srand_seed >> 16) % RAND_MAX);
  49 } /* rand */
  50
  51
  52 /*****************************************************************************
  53
  54     NAME */
  55 #include <stdlib.h>
  56
  57         void srand (
  58
  59 /*  SYNOPSIS */
  60         unsigned int seed)
  61
  62 /*  FUNCTION
  63         Set the starting value for the random number generator rand()
  64         If a seed value is set to a value the same stream of pseudo-random
  65         numbers will be generated by rand() for the same seed value.
  66
  67     INPUTS
  68         seed - New start value
  69
  70     RESULT
  71         None.
  72
  73     NOTES
  74         One seed value per stdc.library is kept which normally corresponds
  75         with per task.
  76
  77     EXAMPLE
  78
  79     BUGS
  80
  81     SEE ALSO
  82         rand()
  83
  84     INTERNALS
  85
  86 ******************************************************************************/
  87 {
  88     struct StdCIntBase *StdCBase = (struct StdCIntBase *)__aros_getbase_StdCBase();
  89
  90     StdCBase->srand_seed = seed;
  91 } /* srand */
  92
  93 static int __rand_seedinit(struct StdCIntBase *StdCBase)
  94 {
  95     // use Xorshift with the suggested coefficients by Marsaglia for
  96     // a 32-bit generator (13, 17, 5)   to set our initial seed.
  97     StdCBase->srand_seed = time(NULL);
  98     StdCBase->srand_seed ^= StdCBase->srand_seed >> 13; // a
  99     StdCBase->srand_seed ^= StdCBase->srand_seed << 17; // b
 100     StdCBase->srand_seed ^= StdCBase->srand_seed >> 5; // c
 101
 102     return 1;
 103 }
 104
 105 ADD2OPENLIB(__rand_seedinit, 0);