/*  slominus.cpp  by K.Tsuru  */
// function ID = 225  DRADIX, BRADIX
/****************
SLong class
operator-()  m-n
******************/
#ifndef SN_H
#include "sn.h"
#endif
SLong operator-(const SLong& m, const SLong& n){
// check radix in LLSub and LLAdd
//  if(m.Radix() != n.Radix()) m.SetError(m.RADIX_ERR, "SL \'-\'", 202);
//This function is also used in Knuth's divide of SInteger class.
//  if((m.Radix() != DRADIX)||(n.Radix() != DRADIX)) m.SetError(m.RADIX_ERR, "SL -", 202);
    int c, s = m.Sign(202) * n.Sign(202);
    SLong r(m.Type(), 0);

    if( !s ){   //One of m and n is zero.
        if( m.Sign() == 0 ){
            r = n;      r.ChangeSign(202);  // r = -n;
            return r;
        } else              return  m;
    } else if( s < 0 ){//diffrent sign
        r = n;          r.ChangeSign(202);  // r = -n;
        return LLAdd(m, r); //The sign is same as that of m and set by LLAdd().
    } else {           //same sign
        c = LLCompare(m, n);

        if(c > 0) return LLSub(m, n); // m > n
        if(c < 0){  //m<n, m-n = -(n-m)
            r = LLSub(n, m);    //r=n-m
            r.ChangeSign(202);      // r = -r;
            return r;
        }
        r.SetZero();
        return r;   // c = 0 : m = n
    }
}