Bit.swift

//===--- Bit.swift - A 1-bit type that can be used as an Index ------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2015 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
//  Used to index CollectionOfOne<T>
//
//===----------------------------------------------------------------------===//

/// A `RandomAccessIndexType` that has two possible values.  Used as
/// the `Index` type for `CollectionOfOne<T>`.
public enum Bit : Int, Comparable, RandomAccessIndexType, _Reflectable {

  public typealias Distance = Int

  case Zero = 0, One = 1

  /// Returns the next consecutive value after `self`.
  ///
  /// - Requires: `self == .Zero`.
  public func successor() -> Bit {
    _precondition(self == .Zero, "Can't increment past one")
    return .One
  }

  /// Returns the previous consecutive value before `self`.
  ///
  /// - Requires: `self != .Zero`.
  public func predecessor() -> Bit {
    _precondition(self == .One, "Can't decrement past zero")
    return .Zero
  }

  public func distanceTo(other: Bit) -> Int {
    return rawValue.distanceTo(other.rawValue)
  }

  public func advancedBy(n: Distance) -> Bit {
    return rawValue.advancedBy(n) > 0 ? One : Zero
  }

  /// Returns a mirror that reflects `self`.
  public func _getMirror() -> _MirrorType {
    return _BitMirror(self)
  }
}

internal struct _BitMirror : _MirrorType {
  let _value: Bit

  init(_ v: Bit) {
    self._value = v
  }

  var value: Any { return _value }

  var valueType: Any.Type { return (_value as Any).dynamicType }

  var objectIdentifier: ObjectIdentifier? { return .None }

  var count: Int { return 0 }

  subscript(i: Int) -> (String, _MirrorType) {
    _preconditionFailure("_MirrorType access out of bounds")
  }

  var summary: String {
    switch _value {
      case .Zero: return ".Zero"
      case .One:  return ".One"
    }
  }

  var quickLookObject: PlaygroundQuickLook? { return .None }

  var disposition: _MirrorDisposition { return .Enum }
}

@warn_unused_result
public func == (lhs: Bit, rhs: Bit) -> Bool {
  return lhs.rawValue == rhs.rawValue
}

@warn_unused_result
public func < (lhs: Bit, rhs: Bit) -> Bool {
  return lhs.rawValue < rhs.rawValue
}

extension Bit : IntegerArithmeticType {
  static func _withOverflow(v: (Int, overflow: Bool)) -> (Bit, overflow: Bool) {
    if let b = Bit(rawValue: v.0) {
      return (b, v.overflow)
    } else {
      return (Bit(rawValue: v.0 % 2)!, true)
    }
  }

  /// Add `lhs` and `rhs`, returning a result and a `Bool` that is
  /// true iff the operation caused an arithmetic overflow.
  public static func addWithOverflow(
    lhs: Bit, _ rhs: Bit
  ) -> (Bit, overflow: Bool) {
    return _withOverflow(Int.addWithOverflow(lhs.rawValue, rhs.rawValue))
  }

  /// Subtract `lhs` and `rhs`, returning a result and a `Bool` that is
  /// true iff the operation caused an arithmetic overflow.
  public static func subtractWithOverflow(
    lhs: Bit, _ rhs: Bit
  ) -> (Bit, overflow: Bool) {
    return _withOverflow(Int.subtractWithOverflow(lhs.rawValue, rhs.rawValue))
  }

  /// Multiply `lhs` and `rhs`, returning a result and a `Bool` that is
  /// true iff the operation caused an arithmetic overflow.
  public static func multiplyWithOverflow(
    lhs: Bit, _ rhs: Bit
  ) -> (Bit, overflow: Bool) {
    return _withOverflow(Int.multiplyWithOverflow(lhs.rawValue, rhs.rawValue))
  }

  /// Divide `lhs` and `rhs`, returning a result and a `Bool` that is
  /// true iff the operation caused an arithmetic overflow.
  public static func divideWithOverflow(
    lhs: Bit, _ rhs: Bit
  ) -> (Bit, overflow: Bool) {
    return _withOverflow(Int.divideWithOverflow(lhs.rawValue, rhs.rawValue))
  }

  /// Divide `lhs` and `rhs`, returning the remainder and a `Bool` that is
  /// true iff the operation caused an arithmetic overflow.
  public static func remainderWithOverflow(
    lhs: Bit, _ rhs: Bit
  ) -> (Bit, overflow: Bool) {
    return _withOverflow(Int.remainderWithOverflow(lhs.rawValue, rhs.rawValue))
  }

  /// Represent this number using Swift's widest native signed integer
  /// type.
  public func toIntMax() -> IntMax {
    return IntMax(rawValue)
  }
}