       _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

  /// 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*/
  ) -> Big {
    let lhsDigitOffset = lhsDigitRange?.startIndex ?? 0
    let rhsDigitOffset = rhsDigitRange?.startIndex ?? 0
