source: trunk/minix/lib/math/sinh.c@ 20

/*
 * (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/sinh.c,v 1.1.1.1 2005/04/21 14:56:26 beng Exp $ */

#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);
}