Expose attosecond representation of Duration (#78202)

* Add Int128 to Duration

* Update stdlib/public/core/Duration.swift

Co-authored-by: Stephen Canon <stephentyrone@gmail.com>

* Add unit tests for duration + attoseconds

* Add docs to duration + attosecond

* Update docs for attoseconds property

* Update stdlib.swift

* Update stdlib.swift

---------

Co-authored-by: Stephen Canon <stephentyrone@gmail.com>

Author: ph1ps

stdlib/public/core/Duration.swift

@@ -99,6 +99,36 @@ extension Duration {
   }
 }
 
+@available(SwiftStdlib 6.0, *)
+extension Duration {
+  /// The number of attoseconds represented by this `Duration`.
+  ///
+  /// This property provides direct access to the underlying number of attoseconds 
+  /// that the current `Duration` represents.
+  ///
+  ///     let d = Duration.seconds(1)
+  ///     print(d.attoseconds) // 1_000_000_000_000_000_000
+  @available(SwiftStdlib 6.0, *)
+  @_alwaysEmitIntoClient
+  public var attoseconds: Int128 {
+    Int128(_low: _low, _high: _high)
+  }
+  
+  /// Construct a `Duration` from the given number of attoseconds.
+  ///
+  /// This directly constructs a `Duration` from the given number of attoseconds.
+  ///
+  ///     let d = Duration(attoseconds: 1_000_000_000_000_000_000)
+  ///     print(d) // 1.0 seconds
+  ///
+  /// - Parameter attoseconds: The total duration expressed in attoseconds.
+  @available(SwiftStdlib 6.0, *)
+  @_alwaysEmitIntoClient
+  public init(attoseconds: Int128) {
+    self.init(_high: attoseconds._high, low: attoseconds._low)
+  }
+}
+
 @available(SwiftStdlib 5.7, *)
 extension Duration {
   /// Construct a `Duration` given a number of seconds represented as a 

test/abi/macOS/arm64/stdlib.swift

@@ -891,3 +891,6 @@ Added: _swift_cvw_destroyMultiPayloadEnumFN
 Added: _swift_cvw_initWithCopyMultiPayloadEnumFN
 Added: _swift_cvw_initWithTakeMultiPayloadEnumFN
 Added: _swift_cvw_initializeBufferWithCopyOfBufferMultiPayloadEnumFN
+
+// SE-0457 Expose attosecond representation of Duration
+Added: _$ss8DurationV11attosecondss6Int128VvpMV

test/abi/macOS/x86_64/stdlib.swift

@@ -892,3 +892,6 @@ Added: _swift_cvw_destroyMultiPayloadEnumFN
 Added: _swift_cvw_initWithCopyMultiPayloadEnumFN
 Added: _swift_cvw_initWithTakeMultiPayloadEnumFN
 Added: _swift_cvw_initializeBufferWithCopyOfBufferMultiPayloadEnumFN
+
+// SE-0457 Expose attosecond representation of Duration
+Added: _$ss8DurationV11attosecondss6Int128VvpMV

test/stdlib/Duration.swift

@@ -234,4 +234,35 @@ if #available(SwiftStdlib 6.0, *) {
     let _ = Duration.nanoseconds( 170141183460469231731687303716 as Int128)
     #endif
   }
+  
+  suite.test("attoseconds init") {
+    let zero = Duration(attoseconds: 0)
+    expectEqual(zero._high, 0)
+    expectEqual(zero._low, 0)
+    let one = Duration(attoseconds: 1)
+    expectEqual(one._high, 0)
+    expectEqual(one._low, 1)
+    let mone = Duration(attoseconds: -1)
+    expectEqual(mone._high, -1)
+    expectEqual(mone._low, .max)
+    let max = Duration(attoseconds: .max)
+    expectEqual(max._high, 9_223_372_036_854_775_807)
+    expectEqual(max._low, 18_446_744_073_709_551_615)
+    let min = Duration(attoseconds: .min)
+    expectEqual(min._high, -9_223_372_036_854_775_808)
+    expectEqual(min._low, 0)
+  }
+  
+  suite.test("attoseconds var") {
+    let zero = Duration(_high: 0, low: 0)
+    expectEqual(zero.attoseconds, 0)
+    let one = Duration(_high: 0, low: 1)
+    expectEqual(one.attoseconds, 1)
+    let mone = Duration(_high: -1, low: .max)
+    expectEqual(mone.attoseconds, -1)
+    let max = Duration(_high: 9_223_372_036_854_775_807, low: 18_446_744_073_709_551_615)
+    expectEqual(max.attoseconds, .max)
+    let min = Duration(_high: -9_223_372_036_854_775_808, low: 0)
+    expectEqual(min.attoseconds, .min)
+  }
 }