gnulib/lib/ldexpl.c

/* Emulation for ldexpl.
   Contributed by Paolo Bonzini

   Copyright 2002, 2003, 2007 Free Software Foundation, Inc.

   This file is part of gnulib.

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

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License along
   with this program; if not, write to the Free Software Foundation,
   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */

#include <config.h>

/* Specification.  */
#include <math.h>

#include <float.h>
#include "fpucw.h"
#include "isnanl.h"

long double
ldexpl(long double x, int exp)
{
  long double factor;
  int bit;
  DECL_LONG_DOUBLE_ROUNDING

  BEGIN_LONG_DOUBLE_ROUNDING ();

  /* Check for zero, nan and infinity. */
  if (!(isnanl (x) || x + x == x))
    {
      if (exp < 0)
	{
	  exp = -exp;
	  factor = 0.5L;
	}
      else
	factor = 2.0L;

      if (exp > 0)
	for (bit = 1;;)
	  {
	    /* Invariant: Here bit = 2^i, factor = 2^-2^i or = 2^2^i,
	       and bit <= exp.  */
	    if (exp & bit)
	      x *= factor;
	    bit <<= 1;
	    if (bit > exp)
	      break;
	    factor = factor * factor;
	  }
    }

  END_LONG_DOUBLE_ROUNDING ();

  return x;
}

#if 0
int
main (void)
{
  long double x;
  int y;
  for (y = 0; y < 29; y++)
    printf ("%5d %.16Lg %.16Lg\n", y, ldexpl(0.8L, y), ldexpl(0.8L, -y) * ldexpl(0.8L, y));
}
#endif