s_ilogb.c

glibc 2.9,最新版的C语言库函数

/* @(#)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.
 * ====================================================
 */

#if defined(LIBM_SCCS) && !defined(lint)
static char rcsid[] = "$NetBSD: s_ilogb.c,v 1.9 1995/05/10 20:47:28 jtc Exp $";
#endif

/* ilogb(double x)
 * return the binary exponent of non-zero x
 * ilogb(0) = FP_ILOGB0
 * ilogb(NaN) = FP_ILOGBNAN (no signal is raised)
 * ilogb(+-Inf) = INT_MAX (no signal is raised)
 */

#include <limits.h>
#include "math.h"
#include "math_private.h"

#ifdef __STDC__
	int __ilogb(double x)
#else
	int __ilogb(x)
	double x;
#endif
{
	int32_t hx,lx,ix;

	GET_HIGH_WORD(hx,x);
	hx &= 0x7fffffff;
	if(hx<0x00100000) {
	    GET_LOW_WORD(lx,x);
	    if((hx|lx)==0)
		return FP_ILOGB0;	/* ilogb(0) = FP_ILOGB0 */
	    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 if (FP_ILOGBNAN != INT_MAX) {
	    /* ISO C99 requires ilogb(+-Inf) == INT_MAX.  */
	    GET_LOW_WORD(lx,x);
	    if(((hx^0x7ff00000)|lx) == 0)
		return INT_MAX;
	}
	return FP_ILOGBNAN;
}
weak_alias (__ilogb, ilogb)
#ifdef NO_LONG_DOUBLE
strong_alias (__ilogb, __ilogbl)
weak_alias (__ilogb, ilogbl)
#endif