/*  sxfxxsub.cpp  by K.Tsuru  */
// function ID = 508    BRADIX
#ifndef SN_H
#include "sn.h"
#endif
static const char* func = "XXSub";
/********************************************************
SDecimal class
Provides m-n where both have the same sign and |m| > |n|.
Signs are not examined for speed.
*********************************************************/
void XXSub(const SDecimal& m, const SDecimal& n, SDecimal& result)
{
    int msign = m.Sign(), nsign = n.Sign(), sgn = msign*nsign;
    if(sgn == 0){
        if(msign) result = m;
        else {
            result = n;     result.SetSign(-nsign);     // result = -n
        }
        return;
    }
// m and n must have the same sign and the same size.
    if(sgn < 0) m.SetError(m.SIGN_ERR, func, 508);
    if( (m.figure.size() != n.figure.size())
        || (result.figure.size() != n.figure.size()) || (m.aTail > n.aTail) )
        m.SetError(m.SYNTAX_ERR, func, 508);

    uint rh = max(m.Head(), n.Head());  // aHead --> Head() since ver 2.191
    uint rt = m.aTail;  // m >= n
    fType* rv = result.figure.Elements();
    const fType* mv = m.ReadFigures();
    const fType* nv = n.ReadFigures();
#ifndef NDEBUG
result.figure(rh);
#endif
    fType u = 0;
    for(int i = rh; i >= (int)rt; i--) {
        u = mv[i] - nv[i] - u;
        rv[i] = u & BRADIX1;
        u = u >> BRADIX_BITS;
    }
// rv[-1] = u;
    if(u) m.SetError(m.SYNTAX_ERR, func, 508);  // m < n

//Clear the outside of above roop.
    if(result.aHead > rh) result.figure.clear(rh+1, result.aHead);
    if(result.aTail < rt) result.figure.clear(result.aTail, rt-1);

//Decide the figure position.
    uint j = rt;
    while( !rv[j] && (j < rh) ) j++;
    if(j == rh){
        result.aTail =  result.aHead = rh;
        result.SetSign(rv[rh] ? msign : 0);
    } else {
        result.aTail = j;
        while(!rv[rh]) rh--;    //There is rv[rh] != 0 anywhere.
        result.aHead = rh;
        result.SetSign(msign);
    }
}