s_logb.c

来自「This is a resource based on j2me embedde」· C语言 代码 · 共 54 行

/*
 * @(#)s_logb.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. 
 *
 */


/*
 * double logb(x)
 * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
 * Use ilogb instead.
 */

#include "fdlibm.h"

#ifdef __STDC__
	double logb(double x)
#else
	double logb(x)
	double x;
#endif
{
	int lx,ix;
	ix = (__HI(x))&0x7fffffff;	/* high |x| */
	lx = __LO(x);			/* low x */
	if((ix|lx)==0) return -1.0/fabs(x);
	if(ix>=0x7ff00000) return x*x;
	if((ix>>=20)==0) 			/* IEEE 754 logb */
		return -1022.0;
	else
		return (double) (ix-1023);
}