Subversion Repositories openrisc_2011-10-31

/* @(#)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_LOG2_E)
. #define log2f(x) (logf (x) / (float) _M_LOG2_E)
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_LOG2_E);
}
 
#endif /* defined(_DOUBLE_IS_32BITS) */