stdlib/erand48_r.c

   1 /* Copyright (C) 1995, 1997 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 not,
  17    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18    Boston, MA 02111-1307, USA.  */
  19
  20 #include <ieee754.h>
  21 #include <stdlib.h>
  22 #include <limits.h>
  23
  24
  25 int
  26 erand48_r (xsubi, buffer, result)
  27      unsigned short int xsubi[3];
  28      struct drand48_data *buffer;
  29      double *result;
  30 {
  31   union ieee754_double temp;
  32
  33   /* Compute next state.  */
  34   if (__drand48_iterate (xsubi, buffer) < 0)
  35     return -1;
  36
  37   /* Construct a positive double with the 48 random bits distributed over
  38      its fractional part so the resulting FP number is [0.0,1.0).  */
  39
  40 #if USHRT_MAX == 65535
  41   temp.ieee.negative = 0;
  42   temp.ieee.exponent = IEEE754_DOUBLE_BIAS - 1;
  43   temp.ieee.mantissa0 = (xsubi[2] << 4) | (xsubi[1] >> 12);
  44   temp.ieee.mantissa1 = ((xsubi[1] & 0xfff) << 20) | (xsubi[0] << 4);
  45   /* Please note the lower 4 bits of mantissa1 are always 0.  */
  46   *result = temp.d;
  47 #else
  48 # error Unsupported size of short int
  49 #endif
  50
  51   return 0;
  52 }