s_modf.c

来自「This is a resource based on j2me embedde」· C语言 代码 · 共 95 行

/*
 * @(#)s_modf.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. 
 *
 */

/*
 * modf(double x, double *iptr)
 * return fraction part of x, and return x's integral part in *iptr.
 * Method:
 *	Bit twiddling.
 *
 * Exception:
 *	No exception.
 */

#include "fdlibm.h"

#ifdef __STDC__
static const double one = 1.0;
#else
static double one = 1.0;
#endif

#ifdef __STDC__
	double modf(double x, double *iptr)
#else
	double modf(x, iptr)
	double x,*iptr;
#endif
{
	int i0,i1,j0;
	unsigned i;
	i0 =  __HI(x);		/* high x */
	i1 =  __LO(x);		/* low  x */
	j0 = ((i0>>20)&0x7ff)-0x3ff;	/* exponent of x */
	if(j0<20) {			/* integer part in high x */
	    if(j0<0) {			/* |x|<1 */
		__HIp(iptr) = i0&0x80000000;
		__LOp(iptr) = 0;		/* *iptr = +-0 */
		return x;
	    } else {
		i = (0x000fffff)>>j0;
		if(((i0&i)|i1)==0) {		/* x is integral */
		    *iptr = x;
		    __HI(x) &= 0x80000000;
		    __LO(x)  = 0;	/* return +-0 */
		    return x;
		} else {
		    __HIp(iptr) = i0&(~i);
		    __LOp(iptr) = 0;
		    return x - *iptr;
		}
	    }
	} else if (j0>51) {		/* no fraction part */
	    *iptr = x*one;
	    __HI(x) &= 0x80000000;
	    __LO(x)  = 0;	/* return +-0 */
	    return x;
	} else {			/* fraction part in low x */
	    i = ((unsigned)(0xffffffff))>>(j0-20);
	    if((i1&i)==0) { 		/* x is integral */
		*iptr = x;
		__HI(x) &= 0x80000000;
		__LO(x)  = 0;	/* return +-0 */
		return x;
	    } else {
		__HIp(iptr) = i0;
		__LOp(iptr) = i1&(~i);
		return x - *iptr;
	    }
	}
}