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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
SYNOPSIS
#include <math.h>
int ilogb(double <[val]>);
int ilogbf(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 <<FP_ILOGB0>>.
If <[val]> is infinite, they return <<INT_MAX>>.
If <[val]> is NaN, they return <<FP_ILOGBNAN>>.
(<<FP_ILOGB0>> and <<FP_ILOGBNAN>> are defined in math.h, but in turn are
defined as INT_MIN or INT_MAX from limits.h. The value of FP_ILOGB0 may be
either INT_MIN or -INT_MAX. The value of FP_ILOGBNAN may be either INT_MAX or
INT_MIN.)
@comment The bugs might not be worth noting, given the mass non-C99/POSIX
@comment behavior of much of the Newlib math library.
@comment BUGS
@comment On errors, errno is not set per C99 and POSIX requirements even if
@comment (math_errhandling & MATH_ERRNO) is non-zero.
PORTABILITY
C99, POSIX
*/
/* ilogb(double x)
* return the binary exponent of non-zero x
* ilogb(0) = 0x80000001
* ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
*/
#include <limits.h>
#include "fdlibm.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 FP_ILOGB0; /* ilogb(0) = special case error */
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;
#if FP_ILOGBNAN != INT_MAX
else if (hx>0x7ff00000) return FP_ILOGBNAN; /* NAN */
#endif
else return INT_MAX; /* infinite (or, possibly, NAN) */
}
#endif /* _DOUBLE_IS_32BITS */
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