erand48_r.c

来自「Axis 221 camera embedded programing inte」· C语言 代码 · 共 52 行

/* Copyright (C) 1995, 1997, 2001 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <[e-mail] <mailto:[e-mail]>>, August 1995.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; 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>

extern int __drand48_iterate(unsigned short xsubi[3], 
	struct drand48_data *buffer);


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).  */

    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);

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

    return 0;
}