/*  sdftnhbs.cpp  by K.Tsuru  */
// function ID 3327 DRADIX since ver 2.18
/*****************************************
SDouble class
It provides hyperbolic tangent tanh(x)
using binary splitting method.
for large x rename "TanBS(x)" since version 2.21
*****************************************/
#ifndef SN_H
#include "sn.h"
#endif

SDouble TanhBSLx(const SDouble& x){
    if(x.Sign(3327) == 0) return 0.0;

    double X = doubleD(x, 0);
// check the condition "exp(2*x) < DRADIX^DRADIX_EXP_MAX".
    const double xMax = 0.5*(double)DFIGURES*M_LN10*(double)DRADIX_EXP_MAX;  // = 301759.17.../2
    if( fabs(X) > xMax){    // exp(x) > D^(DRADIX_EXP_MAX)
        if(x.Sign() > 0) return 1.0;
        return -1.0;
    }
    SDouble r;
    if(x.NetRdxExp() <= 0){ // |x| < DRADIX, tanh x = sinh x/sqrt(1+sinh^2 x)
        r = SinhBS(x);
        r = r*RecSqrt(ONE+r*r);
    } else {    //x >= DRADIX
        SDouble  x2;
        x2 = DsMult(x, 2);  // x2 = x*2
        if(x.Sign() > 0){
            x2 = DReciprocal(ONE + ExpBS(x2));  // x2 = 1/(1+exp(2*x))
            r  = ONE - DsMult(x2, 2);         // r  = 1- 2/(1+exp(2*x))
        } else {
            x2 = DReciprocal(ONE + ExpBS(-x2)); // x2 = 1/(1+exp(-2*x))
            r  = DsMult(x2, 2) - ONE;         // r  = 2/(1+exp(-2*x)) -1
        }
    }
    return r;
}