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/* @(#)s_ilogb.c 5.1 93/09/24 */
/*
* ====================================================
* 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
<<ilogb>>, <<ilogbf>>---get exponent of floating-point number
INDEX
ilogb
INDEX
ilogbf
ANSI_SYNOPSIS
#include <math.h>
int ilogb(double <[val]>);
int ilogbf(float <[val]>);
TRAD_SYNOPSIS
#include <math.h>
int ilogb(<[val]>)
double <[val]>;
int ilogbf(<[val]>)
float <[val]>;
DESCRIPTION
All nonzero, normal numbers can be described as <[m]> *
2**<[p]>. <<ilogb>> and <<ilogbf>> examine the argument
<[val]>, and return <[p]>. The functions <<frexp>> and
<<frexpf>> are similar to <<ilogb>> and <<ilogbf>>, but also
return <[m]>.
RETURNS
<<ilogb>> and <<ilogbf>> return the power of two used to form the
floating-point argument. If <[val]> is <<0>>, they return <<-
INT_MAX>> (<<INT_MAX>> is defined in limits.h). If <[val]> is
infinite, or NaN, they return <<INT_MAX>>.
PORTABILITY
Neither <<ilogb>> nor <<ilogbf>> is required by ANSI C or by
the System V Interface Definition (Issue 2). */
/* ilogb(double x)
* return the binary exponent of non-zero x
* ilogb(0) = 0x80000001
* ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
*/
#include "fdlibm.h"
#include <limits.h>
#ifndef _DOUBLE_IS_32BITS
#ifdef __STDC__
int ilogb(double x)
#else
int ilogb(x)
double x;
#endif
{
__int32_t hx,lx,ix;
EXTRACT_WORDS(hx,lx,x);
hx &= 0x7fffffff;
if(hx<0x00100000) {
if((hx|lx)==0)
return - INT_MAX; /* ilogb(0) = 0x80000001 */
else /* subnormal x */
if(hx==0) {
for (ix = -1043; lx>0; lx<<=1) ix -=1;
} else {
for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
}
return ix;
}
else if (hx<0x7ff00000) return (hx>>20)-1023;
else return INT_MAX;
}
#endif /* _DOUBLE_IS_32BITS */
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