w_gamma.c

来自「This is a resource based on j2me embedde」· C语言 代码 · 共 60 行

/*
 * @(#)w_gamma.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 gamma(double x)
 * Return the logarithm of the Gamma function of x.
 *
 * Method: call gamma_r
 */

#include "fdlibm.h"

extern int signgam;

#ifdef __STDC__
	double gamma(double x)
#else
	double gamma(x)
	double x;
#endif
{
#ifdef _IEEE_LIBM
	return __ieee754_gamma_r(x,&signgam);
#else
        double y;
        y = __ieee754_gamma_r(x,&signgam);
        if(_LIB_VERSION == _IEEE_) return y;
        if(!finite(y)&&finite(x)) {
            if(floor(x)==x&&x<=0.0)
                return __kernel_standard(x,x,41); /* gamma pole */
            else
                return __kernel_standard(x,x,40); /* gamma overflow */
        } else
            return y;
#endif
}