/*  sffffsub.cpp  by K.Tsuru  */
// function ID = 711 DARDIX
/*********************************
SFraction class
It provides the subtraction m-n.
See "sfract.h" about the reduction.
**********************************/
#ifndef SN_H
#include "sn.h"
#endif

SFraction FFSub(const SFraction& x, const SFraction& y){
    SFraction z;
#if REDUCE_SIZE==0 //use Knuth's method
    SLong d1, d2, t, xd1;
    d1 = gcdL(x.den, y.den);
    if(d1.IsOne()) {    // d1 == 1
        z.den = x.den*y.den;
        z.num = x.num*y.den - y.num*x.den;
    } else {
        xd1 = x.den/d1;
        t = x.num*(y.den/d1) - y.num*xd1;
        d2 = gcdL(t, d1);
        if(d2.IsOne()){
            z.den = xd1*y.den;
            z.num = t;
        } else {
            z.den = xd1*(y.den/d2);
            z.num = t/d2;
        }
    }
    if( !z.num.Sign(701) ) z.den.SetShort(1);  //It becomes zero.
    z.reduceDone = true;
    return z;
#else
    if(x.ReduceStepByStep()) {
        SLong d1, d2, t, xd1;
        d1 = gcdL(x.den, y.den);
        if(d1.IsOne()) {    // d1 == 1
            z.den = x.den*y.den;
            z.num = x.num*y.den - y.num*x.den;
        } else {
            xd1 = x.den/d1;
            t = x.num*(y.den/d1) - y.num*xd1;
            d2 = gcdL(t, d1);
            if(d2.IsOne()){
                z.den = xd1*y.den;
                z.num = t;
            } else {
                z.den = xd1*(y.den/d2);
                z.num = t/d2;
            }
        }
        if( !z.num.Sign(701) ) z.den.SetShort(1);  //It becomes zero.
        z.reduceDone = true;
        return z;
    } else {
        z.den = x.den*y.den;
        z.num = x.num*y.den - y.num*x.den;
        z.reduce(false);
        return z;
    }
#endif
}