 func append(_ N: Int, bytes count: Int, to data: Data) {
   let bytes = malloc(count).assumingMemoryBound(to: UInt8.self)
   defer { free(bytes) }
-  for _ in 0..<10000*N {
+  for _ in 1...N {
     var copy = data
     copy.append(bytes, count: count)
   }

  var copy = data
  let count = data.count + extra
  let orig = data.count
  for _ in 0..<10000*N {
    copy.count = count
    copy.count = orig
  }


@inline(never)
func withUnsafeBytes(_ N: Int, data: Data) {
  for _ in 1...N {
    data.withUnsafeBytes { (ptr: UnsafePointer<UInt8>) in
      blackHole(ptr.pointee)
    }
