/*  scfcosbs.cpp  by K.Tsuru  */
// function ID = 9121 since ver.2.18
/*****************************************
SComplex class
It returns cos(z) using binary splitting method.
Let z = x+iy,
cos(z) = cos(x)*cosh(y)-i*sin(x)sinh(y).
*****************************************/
#ifndef SN_H
#include "sn.h"
#endif
SComplex CcosBS(const SComplex& z){
    SDouble c, s, ch, sh;
    CosSinBS(z.Real(), c, s);   // c = cos(x), s = sin(x)
    SDouble e, r;
    int is = z.Imag().Sign(9121);

    if(is > 0) {
        e = ExpBS(z.Imag());    // = exp(y)
        r = 1/e;
        ch = DDiv2(e + r);  // = cosh(y)
        sh = ch - e;        // = -sinh(y)
    } else if(is == 0) {
        ch = 1.0;       sh = 0.0;
    } else {
        e = ExpBS(-z.Imag());   // = exp(-y)
        r = ONE/e;
        ch = DDiv2(e + r);  // = cosh(-y)
        sh = ch - r;        // = -sinh(-y)
    }
    return SComplex(c * ch, s * sh);
}