ack/lang/cem/libcc.ansi/pure/math/sinh.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 <float.h>
#include <errno.h>
#include "localmath.h"

static double
sinh_cosh(double x, int cosh_flag)
{
	/*	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 (__IsNan(x))
	{
		errno = EDOM;
		return 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_VAL;
		}
	}
	else
	{
		double z = exp(y);

		x = 0.5 * (z + (cosh_flag ? 1.0 : -1.0) / z);
	}
	return negative ? -x : x;
}

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

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