/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

/* Tanh(x)
 * Return the Hyperbolic Tangent of x
 *
 * Method :
 *                                     x    -x
 *                                    e  - e
 *      0. tanh(x) is defined to be -----------
 *                                     x    -x
 *                                    e  + e
 *      1. reduce x to non-negative by tanh(-x) = -tanh(x).
 *      2.  0      <= x <  2**-28 : tanh(x) := x with inexact if x != 0
 *                                              -t
 *          2**-28 <= x <  1      : tanh(x) := -----; t = expm1(-2x)
 *                                             t + 2
 *                                                   2
 *          1      <= x <  22     : tanh(x) := 1 - -----; t = expm1(2x)
 *                                                 t + 2
 *          22     <= x <= INF    : tanh(x) := 1.
 *
 * Special cases:
 *      tanh(NaN) is NaN;
 *      only tanh(0)=0 is exact for finite argument.
 */

#include <float.h>

#include "math.h"
#include "math_private.h"

static const volatile double tiny = 1.0e-300;
static const double one = 1.0, two = 2.0, huge = 1.0e300;

double
tanh(double x)
{
        double t,z;
        int32_t jx,ix;

        GET_HIGH_WORD(jx,x);
        ix = jx&0x7fffffff;

    /* x is INF or NaN */
        if(ix>=0x7ff00000) {
            if (jx>=0) return one/x+one;    /* tanh(+-inf)=+-1 */
            else       return one/x-one;    /* tanh(NaN) = NaN */
        }

    /* |x| < 22 */
        if (ix < 0x40360000) {          /* |x|<22 */
            if (ix<0x3e300000) {        /* |x|<2**-28 */
                if(huge+x>one) return x; /* tanh(tiny) = tiny with inexact */
            }
            if (ix>=0x3ff00000) {       /* |x|>=1  */
                t = expm1(two*fabs(x));
                z = one - two/(t+two);
            } else {
                t = expm1(-two*fabs(x));
                z= -t/(t+two);
            }
    /* |x| >= 22, return +-1 */
        } else {
            z = one - tiny;             /* raise inexact flag */
        }
        return (jx>=0)? z: -z;
}

#if (LDBL_MANT_DIG == 53)
__weak_reference(tanh, tanhl);
#endif