FileMemoryCache.swift

func data(for byteRange: CountableRange<Int>) -> DispatchData? {
  // …
  guard let byteRangePointer = malloc(byteRange.count) else { return nil }
  for storageItem in intersectingItems {
    let rangeToCopyInData: CountableRange<Int> = {
      switch (byteRange.contains(storageItem.byteRange.startIndex), byteRange.contains(storageItem.byteRange.endIndex - 1)) {
      case (true, true):
        // Everything: |+++++++++++++|
        return 0..<storageItem.byteRange.count
      case (false, true):
        // End: |---++++++++++|
        return byteRange.startIndex - storageItem.byteRange.startIndex..<storageItem.byteRange.count
      case (true, false):
        // Start: |++++++++++---|
        return 0..<byteRange.endIndex - storageItem.byteRange.startIndex
      case (false, false):
        // Middle: |---+++++++---|
        return byteRange.startIndex - storageItem.byteRange.startIndex..<byteRange.endIndex - storageItem.byteRange.startIndex
      }
    }()
    // Find the byte range in the allocated memory range where to copy the cached data section
    let destinationByteIndex = storageItem.byteRange.startIndex - byteRange.startIndex + rangeToCopyInData.startIndex
    let destinationPointer = byteRangePointer.advanced(by: destinationByteIndex)
    let destinationBufferPointer = UnsafeMutableRawBufferPointer(start: destinationPointer, count: rangeToCopyInData.count)
    storageItem.data.copyBytes(to: destinationBufferPointer, from: rangeToCopyInData)
            
    // Ignore remaining intersections because everything is copied
    if destinationByteIndex + rangeToCopyInData.count >= byteRange.endIndex {
      break
    }
  }
  let byteRangeBufferPointer = UnsafeRawBufferPointer(start: byteRangePointer, count: byteRange.count)
  return DispatchData(bytesNoCopy: byteRangeBufferPointer, deallocator: .free)
}