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/* Returns the base 2 logarithmic function of x
Copyright (C) 2006 IBM Corporation.
Copyright (C) 2007-2015 Free Software Foundation, Inc.
This file is part of the Decimal Floating Point C Library.
Author(s): Joseph Kerian <jkerian@us.ibm.com>
The Decimal Floating Point C Library is free software; you can
redistribute it and/or modify it under the terms of the GNU Lesser
General Public License version 2.1.
The Decimal Floating Point 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 version 2.1 for more details.
You should have received a copy of the GNU Lesser General Public
License version 2.1 along with the Decimal Floating Point C Library;
if not, write to the Free Software Foundation, Inc., 59 Temple Place,
Suite 330, Boston, MA 02111-1307 USA.
Please see libdfp/COPYING.txt for more information. */
#ifndef _DECIMAL_SIZE
# include <decimal32.h>
# define _DECIMAL_SIZE 32
#endif
#include <decContext.h>
#include <decNumber.h>
#include <math.h>
#include <errno.h>
#include <decNumberMath.h>
#define FUNCTION_NAME log2
#include <dfpmacro.h>
static DEC_TYPE
IEEE_FUNCTION_NAME (DEC_TYPE x)
{
decContext context;
decNumber dn_result;
DEC_TYPE result;
decNumber dn_x;
decNumber dn_two;
decNumber dn_logtwo;
decNumber dn_logx;
DEC_TYPE two = DFP_CONSTANT(2.0);
FUNC_CONVERT_TO_DN (&x, &dn_x);
FUNC_CONVERT_TO_DN (&two, &dn_two);
if (decNumberIsNaN (&dn_x))
return x+x;
if (decNumberIsZero (&dn_x)) /* If x == 0: Pole Error */
{
DFP_EXCEPT (FE_DIVBYZERO);
return -DFP_HUGE_VAL;
}
if (decNumberIsNegative (&dn_x)) /* If x < 0,: Domain Error */
{
DFP_EXCEPT (FE_INVALID);
return DFP_NAN;
}
if (decNumberIsInfinite (&dn_x))
return x;
decContextDefault (&context, DEFAULT_CONTEXT);
// log_2 (x) = log_10 (x) / log_10 (2)
decNumberLog10 (&dn_logx, &dn_x, &context);
decNumberLog10 (&dn_logtwo, &dn_two, &context);
decNumberDivide (&dn_result, &dn_logx, &dn_logtwo, &context);
FUNC_CONVERT_FROM_DN (&dn_result, &result, &context);
return result;
}
DEC_TYPE
INTERNAL_FUNCTION_NAME (DEC_TYPE x)
{
DEC_TYPE z = IEEE_FUNCTION_NAME (x);
if (x == DFP_CONSTANT(0.0))
DFP_ERRNO (ERANGE);
if (x < DFP_CONSTANT(0.0))
DFP_ERRNO (EDOM);
return z;
}
weak_alias (INTERNAL_FUNCTION_NAME, EXTERNAL_FUNCTION_NAME)
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