function barrettReduce(x) {
  var self = this
  x.drShiftTo(self.m.t - 1, self.r2)
  if (x.t > self.m.t + 1) {
    x.t = self.m.t + 1
    x.clamp()
  }
  self.mu.multiplyUpperTo(self.r2, self.m.t + 1, self.q3)
  self.m.multiplyLowerTo(self.q3, self.m.t + 1, self.r2)
  while (x.compareTo(self.r2) < 0) x.dAddOffset(1, self.m.t + 1)
  x.subTo(self.r2, x)
  while (x.compareTo(self.m) >= 0) x.subTo(self.m, x)
}