src/bigi/lib/bigi.js
function montRevert(x) {
  var r = new BigInteger()
  x.copyTo(r)
  this.reduce(r)
  return r
}
function montRevert(x) {
  var r = new BigInteger()
  x.copyTo(r)
  this.reduce(r)
  return r
}
x/R mod m