107 lines
2.6 KiB
C
107 lines
2.6 KiB
C
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/* @(#)s_ilogb.c 5.1 93/09/24 */
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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/*
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FUNCTION
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<<ilogb>>, <<ilogbf>>---get exponent of floating-point number
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INDEX
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ilogb
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INDEX
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ilogbf
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ANSI_SYNOPSIS
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#include <math.h>
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int ilogb(double <[val]>);
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int ilogbf(float <[val]>);
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TRAD_SYNOPSIS
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#include <math.h>
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int ilogb(<[val]>)
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double <[val]>;
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int ilogbf(<[val]>)
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float <[val]>;
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DESCRIPTION
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All nonzero, normal numbers can be described as <[m]> *
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2**<[p]>. <<ilogb>> and <<ilogbf>> examine the argument
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<[val]>, and return <[p]>. The functions <<frexp>> and
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<<frexpf>> are similar to <<ilogb>> and <<ilogbf>>, but also
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return <[m]>.
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RETURNS
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<<ilogb>> and <<ilogbf>> return the power of two used to form the
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floating-point argument.
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If <[val]> is <<0>>, they return <<FP_ILOGB0>>.
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If <[val]> is infinite, they return <<INT_MAX>>.
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If <[val]> is NaN, they return <<FP_ILOGBNAN>>.
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(<<FP_ILOGB0>> and <<FP_ILOGBNAN>> are defined in math.h, but in turn are
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defined as INT_MIN or INT_MAX from limits.h. The value of FP_ILOGB0 may be
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either INT_MIN or -INT_MAX. The value of FP_ILOGBNAN may be either INT_MAX or
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INT_MIN.)
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@comment The bugs might not be worth noting, given the mass non-C99/POSIX
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@comment behavior of much of the Newlib math library.
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@comment BUGS
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@comment On errors, errno is not set per C99 and POSIX requirements even if
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@comment (math_errhandling & MATH_ERRNO) is non-zero.
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PORTABILITY
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C99, POSIX
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*/
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/* ilogb(double x)
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* return the binary exponent of non-zero x
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* ilogb(0) = 0x80000001
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* ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
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*/
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#include <limits.h>
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#include "fdlibm.h"
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#ifndef _DOUBLE_IS_32BITS
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#ifdef __STDC__
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int ilogb(double x)
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#else
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int ilogb(x)
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double x;
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#endif
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{
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__int32_t hx,lx,ix;
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EXTRACT_WORDS(hx,lx,x);
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hx &= 0x7fffffff;
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if(hx<0x00100000) {
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if((hx|lx)==0)
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return FP_ILOGB0; /* ilogb(0) = special case error */
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else /* subnormal x */
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if(hx==0) {
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for (ix = -1043; lx>0; lx<<=1) ix -=1;
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} else {
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for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
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}
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return ix;
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}
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else if (hx<0x7ff00000) return (hx>>20)-1023;
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#if FP_ILOGBNAN != INT_MAX
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else if (hx>0x7ff00000) return FP_ILOGBNAN; /* NAN */
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#endif
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else return INT_MAX; /* infinite (or, possibly, NAN) */
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}
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#endif /* _DOUBLE_IS_32BITS */
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