ack/lang/cem/libcc/math/asin.c

/*
 * (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
 */

/* $Header$ */

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

extern int errno;

static double
asin_acos(x, cosfl)
	double x;
{
	int	negative = x < 0;
	int	i;
	double	g;
	extern double	sqrt();
	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 (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(x)
	double x;
{
	return asin_acos(x, 0);
}

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