/*  sdflog1x.cpp  by K.Tsuru  */
// function ID 3403
/***********************************************************************
SDouble class
It provides the natulal logalithm by the series
 calculate log(1-x) = -x(1 + x/2 + x^2/3 +....) = Log1_X(x),
where |x| must be much less than one(|x|<1.0/DRADIX) and 'x' can be negative.
It is better to use the series
 log(1-x) = -(x + x^2/2 + x^3/3 +....)
for the precision.
************************************************************************/
#ifndef SN_H
#include "sn.h"
#endif
static const char* const func = "Log1_X";
SDouble Log1_X(const SDouble& x){
    SDouble sum(x), xn(x*x), delta;

    if(x.NetRdxExp() >= 0) x.SetError(x.OUT_OF_RANGE, func, 3403);

    sum.FixedPoint(sum.RdxExp());
    ulong k = 2, mt = x.SlOpMaxValue();

    do{
        delta = DsDiv(xn, k);
        if(delta.Sign(3403) == 0) break;
        sum += delta;
        xn *= x;
        if( (k++) >= mt ){
            sum.SetError(sum.NOT_CONVERGE, func, -3403);
            break;
        }
    }while(xn.Sign(3403));

    sum.PointFree();
    sum.Reform(3403);
    x.upToTerm = k;
    sum.ChangeSign();
    return sum;
}