/*  slmlsmns.cpp  by K.Tsuru  */
// function ID = 234
/********************************************************************
SLong class
It subtracts a positive short implemented for the decrement operator.
The statement
    return (*this = *this - a);
has a large overhead, because it calls a constructor SLong(a).
*********************************************************************/
#ifndef SN_H
#include "sn.h"
#endif
void SLong::LsMinus(fType a){
    if(!a) return;
    if(Sign(234) < 0){      // -x - a  = -(x+a)
        SetSign(1); LsAdd(a);   SetSign(-1);
        return;
    }
    if(aHead == 0){ //one figure including a=0
        long r = (long)figure[0]-(long)a;
        SetLong(r);     return;
    }
// aHead >0, aTail >= 0, sign > 0
    fType rdx = Radix();
    int r = (int)rdx-(int)a;
    if(figure[0] >= a){
        figure[0] -= a;
        while(figure[aTail] == 0) aTail++;
    } else if(r > 0){   //figure[0] < a < radix
        //*this does not become negative because aHead > 0.
        fType rdx1 = rdx - 1;
        figure[aTail]--;    //It borrows one from upper.
        if(figure[aHead] == 0) aHead--; // figure[aHead] == 1 && aHead == aTail
        for(uint i = 1u; i < aTail; i++) figure[i] = rdx1;
        figure[0] = (fType)r;       aTail = 0;  // r > 0
        if( 2u*(aHead+1) <= figure.size() ) DoCutDown();
    } else {    //a >= radix
        *this -= (double)a;
    }
}