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[stdlib] Update documentation of {U}Int128 types #74775

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merged 1 commit into from
Jun 27, 2024
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[stdlib] Update documentation of {U}Int128 types #74775

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26 changes: 16 additions & 10 deletions stdlib/public/core/Int128.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -10,16 +10,16 @@
//
//===----------------------------------------------------------------------===//

// MARK: - Memory layout
// MARK: Memory layout

/// A 128-bit signed integer type.
/// A 128-bit signed integer value type.
@available(SwiftStdlib 6.0, *)
@frozen
public struct Int128: Sendable {
#if _pointerBitWidth(_64) || arch(arm64_32)
// On 64-bit platforms (including arm64_32 and any similar targets with
// 32b pointers but HW-backed 64b integers), the layout is simply that
// of `Builtin.Int128`.
#if _pointerBitWidth(_64) || arch(arm64_32)
public var _value: Builtin.Int128

@available(SwiftStdlib 6.0, *)
Expand All @@ -45,25 +45,23 @@ public struct Int128: Sendable {
@_transparent
public init(_low: UInt64, _high: Int64) {
#if _endian(little)
self = unsafeBitCast((_low, _high), to: Int128.self)
self = unsafeBitCast((_low, _high), to: Self.self)
#else
self = unsafeBitCast((_high, _low), to: Int128.self)
self = unsafeBitCast((_high, _low), to: Self.self)
#endif
}

#else
// On 32-bit platforms, we don't want to use Builtin.Int128 for layout
// because it would be 16B aligned, which is excessive for such targets
// (and generally incompatible with C's `_BitInt(128)`). Instead we lay
// out the type as two `UInt64` fields--note that we have to be careful
// out the type as two `{U}Int64` fields--note that we have to be careful
// about endianness in this case.
#if _endian(little)
public var _low: UInt64

public var _high: Int64
#else
public var _high: Int64

public var _low: UInt64
#endif

Expand Down Expand Up @@ -94,6 +92,16 @@ public struct Int128: Sendable {
}
#endif

/// Creates a new instance with the same memory representation as the given
/// value.
///
/// This initializer does not perform any range or overflow checking. The
/// resulting instance may not have the same numeric value as
/// `bitPattern`---it is only guaranteed to use the same pattern of bits in
/// its binary representation.
///
/// - Parameter bitPattern: A value to use as the source of the new instance's
/// binary representation.
@available(SwiftStdlib 6.0, *)
@_transparent
public init(bitPattern: UInt128) {
Expand All @@ -102,7 +110,6 @@ public struct Int128: Sendable {
}

// MARK: - Constants

@available(SwiftStdlib 6.0, *)
extension Int128 {
@available(SwiftStdlib 6.0, *)
Expand All @@ -125,7 +132,6 @@ extension Int128 {
}

// MARK: - Conversions from other integers

@available(SwiftStdlib 6.0, *)
extension Int128: ExpressibleByIntegerLiteral,
_ExpressibleByBuiltinIntegerLiteral {
Expand Down
18 changes: 13 additions & 5 deletions stdlib/public/core/UInt128.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -10,9 +10,9 @@
//
//===----------------------------------------------------------------------===//

// MARK: - Memory layout
// MARK: Memory layout

/// A 128-bit unsigned integer type.
/// A 128-bit unsigned integer value type.
@available(SwiftStdlib 6.0, *)
@frozen
public struct UInt128: Sendable {
Expand Down Expand Up @@ -59,13 +59,12 @@ public struct UInt128: Sendable {
// about endianness in this case.
#if _endian(little)
public var _low: UInt64

public var _high: UInt64
#else
public var _high: UInt64

public var _low: UInt64
#endif

@available(SwiftStdlib 6.0, *)
@_transparent
public init(_low: UInt64, _high: UInt64) {
Expand Down Expand Up @@ -93,6 +92,16 @@ public struct UInt128: Sendable {
}
#endif

/// Creates a new instance with the same memory representation as the given
/// value.
///
/// This initializer does not perform any range or overflow checking. The
/// resulting instance may not have the same numeric value as
/// `bitPattern`---it is only guaranteed to use the same pattern of bits in
/// its binary representation.
///
/// - Parameter bitPattern: A value to use as the source of the new instance's
/// binary representation.
@available(SwiftStdlib 6.0, *)
@_transparent
public init(bitPattern: Int128) {
Expand Down Expand Up @@ -541,4 +550,3 @@ extension UInt128: FixedWidthInteger, UnsignedInteger {
return Self(_low: _high.byteSwapped, _high: _low.byteSwapped)
}
}