ack/lang/cem/libcc.ansi/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
 */
/* $Id$ */

#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);
}