BitArray.swift

struct BitArray: RandomAccessCollection, MutableCollection {
  typealias Data = (UInt, UInt)
  
  var data: Data = (0, 0)
  
  var startIndex: Int {
    return 0
  }
  
  var endIndex: Int {
    return MemoryLayout<Data>.size * 8
  }
  
  subscript(_ i: Int) -> Bool {
    get {
      return withUnsafeBytes(of: data) { buffer in
        return (buffer[i / 8] >> (i % 8)) & 1 == 1
      }
    }
    set {
      withUnsafeMutableBytes(of: &data) { buffer in
        let v = (1 as UInt8) << (i % 8)
        if newValue {
          buffer[i / 8] |= v
        } else {
          buffer[i / 8] &= ~v
        }
      }
    }
  }
}