/*
 * (c) copyright 1989 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;
extern double	exp();

static double
sinh_cosh(x, cosh_flag)
	double	x;
{
	/*	Algorithm and coefficients from:
			"Software manual for the elementary functions"
			by W.J. Cody and W. Waite, Prentice-Hall, 1980
	*/

	static double p[] = {
		-0.35181283430177117881e+6,
		-0.11563521196851768270e+5,
		-0.16375798202630751372e+3,
		-0.78966127417357099479e+0
	};
	static double q[] = {
		-0.21108770058106271242e+7,
		 0.36162723109421836460e+5,
		-0.27773523119650701167e+3,
		 1.0
	};
	int	negative = x < 0;
	double	y = negative ? -x : x;

	if (! cosh_flag && y <= 1.0) {
		/* ??? check for underflow ??? */
		y = y * y;
		return x + x * y * POLYNOM3(y, p)/POLYNOM3(y,q);
	}

	if (y >= M_LN_MAX_D) {
		/* exp(y) would cause overflow */
#define LNV	0.69316101074218750000e+0
#define VD2M1	0.52820835025874852469e-4
		double	w = y - LNV;
		
		if (w < M_LN_MAX_D+M_LN2-LNV) {
			x = exp(w);
			x += VD2M1 * x;
		}
		else {
			errno = ERANGE;
			x = HUGE;
		}
	}
	else {
		double	z = exp(y);
		
		x = 0.5 * (z + (cosh_flag ? 1.0 : -1.0)/z);
	}
	return negative ? -x : x;
}

double
sinh(x)
	double x;
{
	return sinh_cosh(x, 0);
}

double
cosh(x)
	double x;
{
	if (x < 0) x = -x;
	return sinh_cosh(x, 1);
}
