source: trunk/minix/lib/math/pow.c@ 20

/*
 * (c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
 * See the copyright notice in the ACK home directory, in the file "Copyright".
 *
 * Author: Ceriel J.H. Jacobs
 */
/* $Header: /cvsup/minix/src/lib/math/pow.c,v 1.1.1.1 2005/04/21 14:56:26 beng Exp $ */

#include        <math.h>
#include        <float.h>
#include        <errno.h>
#include        "localmath.h"

double
pow(double x, double y)
{
        /*      Simple version for now. The Cody and Waite book has
                a very complicated, much more precise version, but
                this version has machine-dependent arrays A1 and A2,
                and I don't know yet how to solve this ???
        */
        double dummy;
        int     result_neg = 0;

        if ((x == 0 && y == 0) ||
            (x < 0 && modf(y, &dummy) != 0)) {
                errno = EDOM;
                return 0;
        }

        if (x == 0) return x;

        if (x < 0) {
                if (modf(y/2.0, &dummy) != 0) {
                        /* y was odd */
                        result_neg = 1;
                }
                x = -x;
        }
        x = log(x);

        if (x < 0) {
                x = -x;
                y = -y;
        }
        /* Beware of overflow in the multiplication */
        if (x > 1.0 && y > DBL_MAX/x) {
                errno = ERANGE;
                return result_neg ? -HUGE_VAL : HUGE_VAL;
        }

        x = exp(x * y);
        return result_neg ? -x : x;
}