glibc/stdlib/erand48_r.c

/* Copyright (C) 1995, 1997 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <drepper@gnu.ai.mit.edu>, August 1995.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include <ieee754.h>
#include <stdlib.h>
#include <limits.h>


int
__erand48_r (xsubi, buffer, result)
     unsigned short int xsubi[3];
     struct drand48_data *buffer;
     double *result;
{
  union ieee754_double temp;

  /* Compute next state.  */
  if (__drand48_iterate (xsubi, buffer) < 0)
    return -1;

  /* Construct a positive double with the 48 random bits distributed over
     its fractional part so the resulting FP number is [0.0,1.0).  */

#if USHRT_MAX == 65535
  temp.ieee.negative = 0;
  temp.ieee.exponent = IEEE754_DOUBLE_BIAS;
  temp.ieee.mantissa0 = (xsubi[2] << 4) | (xsubi[1] >> 12);
  temp.ieee.mantissa1 = ((xsubi[1] & 0xfff) << 20) | (xsubi[0] << 4);
#elif USHRT_MAX == 2147483647
  temp.ieee.negative = 0;
  temp.ieee.exponent = IEEE754_DOUBLE_BIAS;
  temp.ieee.mantissa0 = (xsubi[1] << 4) | (xsubi[0] >> 28);
  temp.ieee.mantissa1 = ((xsubi[0] & 0xfffffff) << 4);
#else
# error Unsupported size of short int
#endif

  /* Please note the lower 4 bits of mantissa1 are always 0.  */
  *result = temp.d - 1.0;

  return 0;
}
weak_alias (__erand48_r, erand48_r)