source: trunk/minix/lib/math/asin.c@ 9

/*
 * (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/asin.c,v 1.1.1.1 2005/04/21 14:56:24 beng Exp $ */

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

static double
asin_acos(double x, int cosfl)
{
        int negative = x < 0;
        int     i;
        double  g;
        static double p[] = {
                -0.27368494524164255994e+2,
                 0.57208227877891731407e+2,
                -0.39688862997540877339e+2,
                 0.10152522233806463645e+2,
                -0.69674573447350646411e+0
        };
        static double q[] = {
                -0.16421096714498560795e+3,
                 0.41714430248260412556e+3,
                -0.38186303361750149284e+3,
                 0.15095270841030604719e+3,
                -0.23823859153670238830e+2,
                 1.0
        };

        if (__IsNan(x)) {
                errno = EDOM;
                return x;
        }

        if (negative) {
                x = -x;
        }
        if (x > 0.5) {
                i = 1;
                if (x > 1) {
                        errno = EDOM;
                        return 0;
                }
                g = 0.5 - 0.5 * x;
                x = - sqrt(g);
                x += x;
        }
        else {
                /* ??? avoid underflow ??? */
                i = 0;
                g = x * x;
        }
        x += x * g * POLYNOM4(g, p) / POLYNOM5(g, q);
        if (cosfl) {
                if (! negative) x = -x;
        }
        if ((cosfl == 0) == (i == 1)) {
                x = (x + M_PI_4) + M_PI_4;
        }
        else if (cosfl && negative && i == 1) {
                x = (x + M_PI_2) + M_PI_2;
        }
        if (! cosfl && negative) x = -x;
        return x;
}

double
asin(double x)
{
        return asin_acos(x, 0);
}

double
acos(double x)
{
        return asin_acos(x, 1);
}