mirror of
https://github.com/KolibriOS/kolibrios.git
synced 2024-12-16 03:42:35 +03:00
86 lines
2.1 KiB
C
86 lines
2.1 KiB
C
/* @(#)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
|
|
|
|
ANSI_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.
|
|
|
|
You can use the (non-ANSI) function <<matherr>> to specify error
|
|
handling for these functions, indirectly through the respective <<log>>
|
|
function.
|
|
|
|
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>>. You can control the error behavior via
|
|
<<matherr>>.
|
|
|
|
PORTABILITY
|
|
C99, POSIX, System V Interface Definition (Issue 6).
|
|
*/
|
|
|
|
/*
|
|
* wrapper log2(x)
|
|
*/
|
|
|
|
#include "fdlibm.h"
|
|
#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) */
|