(protected) divide this by m, quotient and remainder to q, r (HAC 14.20) r != q, this != m.  q or r may be null.
function bnpDivRemTo(m,q,r) {
  var pm = m.abs();
  if(pm.t <= 0) return;
  var pt = this.abs();
  if(pt.t < pm.t) {
    if(q != null) q.fromInt(0);
    if(r != null) this.copyTo(r);
    return;
  }
  if(r == null) r = nbi();
  var y = nbi(), ts = this.s, ms = m.s;
  var pm_array = pm.array;
  var nsh = BI_DB-nbits(pm_array[pm.t-1]);	// normalize modulus
  if(nsh > 0) { pm.lShiftTo(nsh,y); pt.lShiftTo(nsh,r); }
  else { pm.copyTo(y); pt.copyTo(r); }
  var ys = y.t;

  var y_array = y.array;
  var y0 = y_array[ys-1];
  if(y0 == 0) return;
  var yt = y0*(1<<BI_F1)+((ys>1)?y_array[ys-2]>>BI_F2:0);
  var d1 = BI_FV/yt, d2 = (1<<BI_F1)/yt, e = 1<<BI_F2;
  var i = r.t, j = i-ys, t = (q==null)?nbi():q;
  y.dlShiftTo(j,t);

  var r_array = r.array;
  if(r.compareTo(t) >= 0) {
    r_array[r.t++] = 1;
    r.subTo(t,r);
  }
  BigInteger.ONE.dlShiftTo(ys,t);
  t.subTo(y,y);	// "negative" y so we can replace sub with am later
  while(y.t < ys) y_array[y.t++] = 0;
  while(--j >= 0) {
    // Estimate quotient digit
    var qd = (r_array[--i]==y0)?BI_DM:Math.floor(r_array[i]*d1+(r_array[i-1]+e)*d2);
    if((r_array[i]+=y.am(0,qd,r,j,0,ys)) < qd) {	// Try it out
      y.dlShiftTo(j,t);
      r.subTo(t,r);
      while(r_array[i] < --qd) r.subTo(t,r);
    }
  }
  if(q != null) {
    r.drShiftTo(ys,q);
    if(ts != ms) BigInteger.ZERO.subTo(q,q);
  }
  r.t = ys;
  r.clamp();
  if(nsh > 0) r.rShiftTo(nsh,r);	// Denormalize remainder
  if(ts < 0) BigInteger.ZERO.subTo(r,r);
}