w_gamma.c

freedos32的源代码

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

#ifndef lint
static char rcsid[] = "$\Id: w_gamma.c,v 1.2 1995/05/30 05:51:04 rgrimes Exp $";
#endif

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

#include "math.h"
#include "math_private.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
}