stdlib/erand48_r.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 <stdlib.h>
  21 #include <limits.h>
  22
  23
  24 int
  25 erand48_r (xsubi, buffer, result)
  26      unsigned short int xsubi[3];
  27      struct drand48_data *buffer;
  28      double *result;
  29 {
  30   /* Compute next state.  */
  31   if (__drand48_iterate (xsubi, buffer) < 0)
  32     return -1;
  33
  34   /* Construct a positive double with the 48 random bits distributed over
  35      its fractional part so the resulting FP number is [0.0,1.0).  */
  36
  37 #if USHRT_MAX == 65535
  38   *result = ((double) xsubi[2] / (1ULL << 48) +
  39              (double) xsubi[1] / (1ULL << 32) +
  40              (double) xsubi[0] / (1ULL << 16));
  41 #else
  42 # error Unsupported size of short int
  43 #endif
  44
  45   return 0;
  46 }