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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift Atomics open source project
//
// Copyright (c) 2023 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
import Builtin
/// A pair of two word sized `UInt`s.
///
/// This type's primary purpose is to be used in double wide atomic operations.
/// On platforms that support it, atomic operations on `WordPair` are done in a
/// single operation for two words. Users can use this type as itself when used
/// on `Atomic`, or it could be used as an intermediate step for custom
/// `AtomicRepresentable` types that are also double wide.
///
/// let atomicPair = Atomic<WordPair>(WordPair(first: 0, second: 0))
/// atomicPair.store(WordPair(first: someVersion, second: .max), ordering: .relaxed)
///
/// When used as an intermediate step for custom `AtomicRepresentable` types, it
/// is critical that their `AtomicRepresentation` be equal to
/// `WordPair.AtomicRepresentation`.
///
/// struct GridPoint {
/// var x: Int
/// var y: Int
/// }
///
/// extension GridPoint: AtomicRepresentable {
/// typealias AtomicRepresentation = WordPair.AtomicRepresentation
///
/// ...
/// }
///
/// - Note: This type only conforms to `AtomicRepresentable` on platforms that
/// support double wide atomics.
@available(SwiftStdlib 6.0, *)
@frozen
public struct WordPair {
/// The first element in this word pair.
public var first: UInt
/// The second element in this word pair.
public var second: UInt
/// Initialize a new `WordPair` value given both individual words.
///
/// - Parameter first: The first word to use in the pair.
/// - Parameter second: The second word to use in the pair.
@available(SwiftStdlib 6.0, *)
@_alwaysEmitIntoClient
@_transparent
public init(first: UInt, second: UInt) {
self.first = first
self.second = second
}
}
#if (_pointerBitWidth(_32) && _hasAtomicBitWidth(_64)) || (_pointerBitWidth(_64) && _hasAtomicBitWidth(_128))
@available(SwiftStdlib 6.0, *)
extension WordPair: AtomicRepresentable {
#if _pointerBitWidth(_64)
/// The storage representation type that `Self` encodes to and decodes from
/// which is a suitable type when used in atomic operations.
public typealias AtomicRepresentation = _Atomic128BitStorage
#elseif _pointerBitWidth(_32)
/// The storage representation type that `Self` encodes to and decodes from
/// which is a suitable type when used in atomic operations.
public typealias AtomicRepresentation = _Atomic64BitStorage
#else
#error("Unsupported platform")
#endif
/// Destroys a value of `Self` and prepares an `AtomicRepresentation` storage
/// type to be used for atomic operations.
///
/// - Note: This is not an atomic operation. This simply encodes the logical
/// type `Self` into its storage representation suitable for atomic
/// operations, `AtomicRepresentation`.
///
/// - Parameter value: A valid instance of `Self` that's about to be destroyed
/// to encode an instance of its `AtomicRepresentation`.
/// - Returns: The newly encoded `AtomicRepresentation` storage.
@available(SwiftStdlib 6.0, *)
@_alwaysEmitIntoClient
@_transparent
public static func encodeAtomicRepresentation(
_ value: consuming WordPair
) -> AtomicRepresentation {
#if _pointerBitWidth(_64)
var i128 = Builtin.zext_Int64_Int128(value.first._value)
var high128 = Builtin.zext_Int64_Int128(value.second._value)
let highShift = Builtin.zext_Int64_Int128(UInt(64)._value)
high128 = Builtin.shl_Int128(high128, highShift)
i128 = Builtin.or_Int128(i128, high128)
return AtomicRepresentation(i128)
#elseif _pointerBitWidth(_32)
var i64 = Builtin.zext_Int32_Int64(value.first._value)
var high64 = Builtin.zext_Int32_Int64(value.second._value)
let highShift = Builtin.zext_Int32_Int64(UInt(32)._value)
high64 = Builtin.shl_Int64(high64, highShift)
i64 = Builtin.or_Int64(i64, high64)
return AtomicRepresentation(i64)
#else
#error("Unsupported platform")
#endif
}
/// Recovers the logical atomic type `Self` by destroying some
/// `AtomicRepresentation` storage instance returned from an atomic operation.
///
/// - Note: This is not an atomic operation. This simply decodes the storage
/// representation used in atomic operations back into the logical type for
/// normal use, `Self`.
///
/// - Parameter storage: The storage representation for `Self` that's used
/// within atomic operations.
/// - Returns: The newly decoded logical type `Self`.
@available(SwiftStdlib 6.0, *)
@_alwaysEmitIntoClient
@_transparent
public static func decodeAtomicRepresentation(
_ representation: consuming AtomicRepresentation
) -> WordPair {
#if _pointerBitWidth(_64)
let highShift = Builtin.zext_Int64_Int128(UInt(64)._value)
let high128 = Builtin.lshr_Int128(representation._storage, highShift)
let high = Builtin.trunc_Int128_Int64(high128)
let low = Builtin.trunc_Int128_Int64(representation._storage)
#elseif _pointerBitWidth(_32)
let highShift = Builtin.zext_Int32_Int64(UInt(32)._value)
let high64 = Builtin.lshr_Int64(representation._storage, highShift)
let high = Builtin.trunc_Int64_Int32(high64)
let low = Builtin.trunc_Int64_Int32(representation._storage)
#else
#error("Unsupported platform")
#endif
return WordPair(first: UInt(low), second: UInt(high))
}
}
#endif
@available(SwiftStdlib 6.0, *)
extension WordPair: Equatable {
/// Compares two values of this type to determine if they are equivalent to
/// each other.
///
/// - Parameter lhs: The first value to compare.
/// - Parameter rhs: The second value to compare.
/// - Returns: True if both values were equal, or false if they were unequal.
@available(SwiftStdlib 6.0, *)
@_alwaysEmitIntoClient
@_transparent
public static func ==(lhs: WordPair, rhs: WordPair) -> Bool {
lhs.first == rhs.first && lhs.second == rhs.second
}
}
@available(SwiftStdlib 6.0, *)
extension WordPair: Hashable {
/// Hashes the essential components of this value by feeding them into the
/// given hasher.
///
/// - Parameter hasher: The hasher to use when combining the components
/// of this instance.
@available(SwiftStdlib 6.0, *)
@_alwaysEmitIntoClient
@_transparent
public func hash(into hasher: inout Hasher) {
hasher.combine(first)
hasher.combine(second)
}
}
@available(SwiftStdlib 6.0, *)
@_unavailableInEmbedded
extension WordPair: CustomStringConvertible {
/// A string that represents the contents of the word pair.
@available(SwiftStdlib 6.0, *)
public var description: String {
"WordPair(first: \(first), second: \(second))"
}
}
@available(SwiftStdlib 6.0, *)
@_unavailableInEmbedded
extension WordPair: CustomDebugStringConvertible {
/// A string that represents the contents of the word pair, suitable for
/// debugging.
@available(SwiftStdlib 6.0, *)
public var debugDescription: String {
"WordPair(first: \(first), second: \(second))"
}
}
@available(SwiftStdlib 6.0, *)
extension WordPair: Sendable {}
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