s_frexp.c

来自「This is a resource based on j2me embedde」· C语言 代码 · 共 72 行

/*
 * @(#)s_frexp.c	1.9 06/10/10
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.  
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
 *   
 * This program is free software; you can redistribute it and/or  
 * modify it under the terms of the GNU General Public License version  
 * 2 only, as published by the Free Software Foundation.   
 *   
 * This program is distributed in the hope that it will be useful, but  
 * WITHOUT ANY WARRANTY; without even the implied warranty of  
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU  
 * General Public License version 2 for more details (a copy is  
 * included at /legal/license.txt).   
 *   
 * You should have received a copy of the GNU General Public License  
 * version 2 along with this work; if not, write to the Free Software  
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  
 * 02110-1301 USA   
 *   
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa  
 * Clara, CA 95054 or visit www.sun.com if you need additional  
 * information or have any questions. 
 *
 */


/*
 * for non-zero x
 *	x = frexp(arg,&exp);
 * return a double fp quantity x such that 0.5 <= |x| <1.0
 * and the corresponding binary exponent "exp". That is
 *	arg = x*2^exp.
 * If arg is inf, 0.0, or NaN, then frexp(arg,&exp) returns arg
 * with *exp=0.
 */

#include "fdlibm.h"

#ifdef __STDC__
static const double
#else
static double
#endif
two54 =  1.80143985094819840000e+16; /* 0x43500000, 0x00000000 */

#ifdef __STDC__
	double frexp(double x, int *eptr)
#else
	double frexp(x, eptr)
	double x; int *eptr;
#endif
{
	int  hx, ix, lx;
	hx = __HI(x);
	ix = 0x7fffffff&hx;
	lx = __LO(x);
	*eptr = 0;
	if(ix>=0x7ff00000||((ix|lx)==0)) return x;	/* 0,inf,nan */
	if (ix<0x00100000) {		/* subnormal */
	    x *= two54;
	    hx = __HI(x);
	    ix = hx&0x7fffffff;
	    *eptr = -54;
	}
	*eptr += (ix>>20)-1022;
	hx = (hx&0x800fffff)|0x3fe00000;
	__HI(x) = hx;
	return x;
}