mirror of
https://github.com/autc04/Retro68.git
synced 2024-12-01 11:52:47 +00:00
98 lines
2.5 KiB
C
98 lines
2.5 KiB
C
|
|
/* @(#)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 */
|