stdlib/drand48-iter.c

   1 /* Copyright (C) 1995 Free Software Foundation, Inc.
   2 This file is part of the GNU C Library.
   3 Contributed by Ulrich Drepper <drepper@gnu.ai.mit.edu>, August 1995.
   4
   5 The GNU C Library is free software; you can redistribute it and/or
   6 modify it under the terms of the GNU Library General Public License as
   7 published by the Free Software Foundation; either version 2 of the
   8 License, or (at your option) any later version.
   9
  10 The GNU C Library is distributed in the hope that it will be useful,
  11 but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13 Library General Public License for more details.
  14
  15 You should have received a copy of the GNU Library General Public
  16 License along with the GNU C Library; see the file COPYING.LIB.  If
  17 not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18 Boston, MA 02111-1307, USA.  */
  19
  20 #include <errno.h>
  21 #include <stdlib.h>
  22
  23
  24 /* Global state for non-reentrent functions.  */
  25 struct drand48_data __libc_drand48_data;
  26
  27
  28 int
  29 __drand48_iterate (xsubi, buffer)
  30      unsigned short int xsubi[3];
  31      struct drand48_data *buffer;
  32 {
  33   /* Be generous for the arguments, detect some errors.  */
  34   if (xsubi == NULL || buffer == NULL)
  35     {
  36       errno = EFAULT;
  37       return -1;
  38     }
  39
  40   /* Initialize buffer, if not yet done.  */
  41   if (!buffer->init)
  42     {
  43       if (sizeof (unsigned short int) == 2)
  44         {
  45           buffer->a[2] = 0x5;
  46           buffer->a[1] = 0xdeec;
  47           buffer->a[0] = 0xe66d;
  48         }
  49       else
  50         {
  51           buffer->a[2] = 0x5deecUL;
  52           buffer->a[1] = 0xe66d0000UL;
  53           buffer->a[0] = 0;
  54         }
  55       buffer->c = 0xb;
  56       buffer->init = 1;
  57     }
  58
  59   /* Do the real work.  We choose a data type which contains at least
  60      48 bits.  Because we compute the modulus it does not care how
  61      many bits really are computed.  */
  62
  63   if (sizeof (long int) >= 6)
  64     {
  65       /* The `long' data type is sufficent.  */
  66       unsigned long int X, a, result;
  67
  68 #define ONE_STEP                                                            \
  69       if (sizeof (unsigned short int) == 2)                                 \
  70         {                                                                   \
  71           X = (xsubi[2] << 16 | xsubi[1]) << 16 | xsubi[0];                 \
  72           a = (buffer->a[2] << 16 | buffer->a[1]) << 16 | buffer->a[0];     \
  73                                                                             \
  74           result = X * a + buffer->c;                                       \
  75                                                                             \
  76           xsubi[0] = result & 0xffff;                                       \
  77           result >>= 16;                                                    \
  78           xsubi[1] = result & 0xffff;                                       \
  79           result >>= 16;                                                    \
  80           xsubi[2] = result & 0xffff;                                       \
  81         }                                                                   \
  82       else                                                                  \
  83         {                                                                   \
  84           X = xsubi[2] << 16 | xsubi[1] >> 16;                              \
  85           a = buffer->a[2] << 16 | buffer->a[1] >> 16;                      \
  86                                                                             \
  87           result = X * a + buffer->c;                                       \
  88                                                                             \
  89           xsubi[0] = result >> 16 & 0xffffffffl;                            \
  90           xsubi[1] = result << 16 & 0xffff0000l;                            \
  91         }
  92       ONE_STEP;
  93     }
  94   else
  95     {
  96       /* We have to use the `long long' data type.  */
  97       unsigned long long int X, a, result;
  98       ONE_STEP;
  99     }
 100
 101   return 0;
 102 }