/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
 */
/*
 * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#pragma weak __coshl = coshl

#include "libm.h"
#include "longdouble.h"

/*
 * COSH(X)
 * RETURN THE HYPERBOLIC COSINE OF X
 *
 * Method :
 *      1. Replace x by |x| (COSH(x) = COSH(-x)).
 *      2.
 *                                                      [ EXP(x) - 1 ]^2
 *          0        <= x <= 0.3465  :  COSH(x) := 1 + -------------------
 *                                                         2*EXP(x)
 *
 *                                                 EXP(x) +  1/EXP(x)
 *          0.3465   <= x <= thresh  :  COSH(x) := -------------------
 *                                                         2
 *          thresh   <= x <= lnovft  :  COSH(x) := EXP(x)/2
 *          lnovft   <= x <  INF     :  COSH(x) := SCALBN(EXP(x-MEP1*ln2),ME)
 *
 *
 * here
 *      0.3465          a number that is near one half of ln2.
 *      thresh          a number such that
 *                              EXP(thresh)+EXP(-thresh)=EXP(thresh)
 *      lnovft          logarithm of the overflow threshold
 *                      = MEP1*ln2 chopped to machine precision.
 *      ME              maximum exponent
 *      MEP1            maximum exponent plus 1
 *
 * Special cases:
 *      COSH(x) is |x| if x is +INF, -INF, or NaN.
 *      only COSH(0)=1 is exact for finite x.
 */

static const long double C[] = {
        0.5L,
        1.0L,
        0.3465L,
        45.0L,
        1.135652340629414394879149e+04L,
        7.004447686242549087858985e-16L,
        2.710505431213761085018632e-20L,                /* 2^-65 */
};

#define half    C[0]
#define one     C[1]
#define thr1    C[2]
#define thr2    C[3]
#define lnovft  C[4]
#define lnovlo  C[5]
#define tinyl   C[6]

long double
coshl(long double x) {
        long double w, t;

        w = fabsl(x);
        if (!finitel(w))
                return (w + w); /* x is INF or NaN */
        if (w < thr1) {
                if (w < tinyl)
                        return (one + w);       /* inexact+directed rounding */
                t = expm1l(w);
                w = one + t;
                w = one + (t * t) / (w + w);
                return (w);
        }
        if (w < thr2) {
                t = expl(w);
                return (half * (t + one / t));
        }
        if (w <= lnovft)
                return (half * expl(w));
        return (scalbnl(expl((w - lnovft) - lnovlo), 16383));
}