function montConvert(x) {
  var r = new BigInteger()
  x.abs()
    .dlShiftTo(this.m.t, r)
  r.divRemTo(this.m, null, r)
  if (x.s < 0 && r.compareTo(BigInteger.ZERO) > 0) this.m.subTo(r, r)
  return r
}