   /// The result of this operation is not canonicalized.
   internal static func _multiplyMagnitude(
     _ lhs: Big, range lhsDigitRange: CountableRange<Int>? = nil,
-    _ rhs: Big, range rhsDigitRange: CountableRange<Int>? = nil,
-    karatsubaThreshold n: Int = /* 16 */ 2
+    _ rhs: Big, range rhsDigitRange: CountableRange<Int>? = nil/*,
+    karatsubaThreshold n: Int = /* 16 */ 2*/
   ) -> Big {
     let lhsDigitOffset = lhsDigitRange?.startIndex ?? 0
     let rhsDigitOffset = rhsDigitRange?.startIndex ?? 0

      _subtractAssignMagnitude(&product, offset: m, z0)
      return product
    }

    var digits = [Digit](repeating: 0, count: lhsDigitCount + rhsDigitCount)


    let rhsDigitCount = rhsDigitRange?.count ?? rhs._magnitude.count
    guard lhsDigitCount > 0 && rhsDigitCount > 0 else { return Big() }

    /*
    precondition(n >= 2, "Karatsuba threshold must be at least 2")
    guard lhsDigitCount < n || rhsDigitCount < n else {
      let m = Swift.max(lhsDigitCount, rhsDigitCount) / 2
