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/* @(#)s_log2.c 5.1 93/09/24 */
/* Modification from s_exp10.c Yaakov Selkowitz 2009. */
/*
* ====================================================
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
*
* Developed at SunPro, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*/
/*
FUNCTION
<<log2>>, <<log2f>>---base 2 logarithm
INDEX
log2
INDEX
log2f
SYNOPSIS
#include <math.h>
double log2(double <[x]>);
float log2f(float <[x]>);
DESCRIPTION
The <<log2>> functions compute the base-2 logarithm of <[x]>. A domain error
occurs if the argument is less than zero. A range error occurs if the
argument is zero.
The Newlib implementations are not full, intrinisic calculations, but
rather are derivatives based on <<log>>. (Accuracy might be slightly off from
a direct calculation.) In addition to functions, they are also implemented as
macros defined in math.h:
. #define log2(x) (log (x) / _M_LN2)
. #define log2f(x) (logf (x) / (float) _M_LN2)
To use the functions instead, just undefine the macros first.
RETURNS
The <<log2>> functions return
@ifnottex
<<log base-2(<[x]>)>>
@end ifnottex
@tex
$log_2(x)$
@end tex
on success.
When <[x]> is zero, the
returned value is <<-HUGE_VAL>> and <<errno>> is set to <<ERANGE>>.
When <[x]> is negative, the returned value is NaN (not a number) and
<<errno>> is set to <<EDOM>>.
PORTABILITY
C99, POSIX, System V Interface Definition (Issue 6).
*/
/*
* wrapper log2(x)
*/
#include "fdlibm.h"
#if __OBSOLETE_MATH
#include <errno.h>
#include <math.h>
#undef log2
#ifndef _DOUBLE_IS_32BITS
#ifdef __STDC__
double log2(double x) /* wrapper log2 */
#else
double log2(x) /* wrapper log2 */
double x;
#endif
{
return (log(x) / M_LN2);
}
#endif /* defined(_DOUBLE_IS_32BITS) */
#endif /* __OBSOLETE_MATH */
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