/*  sxfbcoss.cpp  by K.Tsuru  */
// function ID 5202     BRADIX
#ifndef SN_H
#include "sn.h"
#endif
/***************
SDecimal class
cos x by series
****************/
SDecimal BcosSeries(const SDouble& x){
    SDouble Xsq(x*x);
    SDecimal sum(1.0), xsq, delta, q;
    xsq = q.ConvToBin(Xsq);
    XsDiv(xsq, 2, delta);
    ulong mt = delta.SlOpMaxValue(), n = 3, den;

    XXSub(sum, delta, sum);

    do{
        den = n*(n+1);
        if(den > mt)    break;
        q = delta*xsq;
        XsDiv(q, den, delta);

        if(n & 2) XXAdd(sum, delta, sum);
        else      XXSub(sum, delta, sum);
        n += 2;
    } while(delta.Sign());

    while(delta.Sign()){
        if(n > mt){
            sum.SetError(sum.NOT_CONVERGE,"BcosSeries", -5202);
            break;
        }
        q = delta*xsq;
        XsDiv(q ,n, delta);
        XsDiv(delta, n+1, delta);

        if(n & 2) XXAdd(sum, delta, sum);
        else      XXSub(sum, delta, sum);
        n += 2;
    }
    sum.upToTerm = (long)n/2;
    return sum;
}