Revert 'Adopt Swift 6' (#118)

Author: fboemer

.github/workflows/ci.yml

@@ -37,7 +37,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        swift: ["6.0"]
+        swift: ["5.10", "6.0"]
     name: swift ${{ matrix.swift }} tests
     steps:
     - uses: slashmo/[email protected]

Package.resolved

@@ -1,4 +1,4 @@
-// swift-tools-version: 6.0
+// swift-tools-version: 5.10
 // The swift-tools-version declares the minimum version of Swift required to build this package.
 // Remember to update CI if changing
 
@@ -17,7 +17,9 @@
 // limitations under the License.
 import PackageDescription
 
-let librarySettings: [SwiftSetting] = []
+let librarySettings: [SwiftSetting] = [
+    .enableExperimentalFeature("StrictConcurrency"),
+]
 
 let executableSettings: [SwiftSetting] =
     librarySettings +
@@ -271,9 +273,7 @@ package.targets += [
         ]),
 ]
 
-#if canImport(Darwin)
 // Set the minimum macOS version for the package
 package.platforms = [
-    .macOS(.v15), // Constrained by Swift 6 support for Xcode (https://developer.apple.com/support/xcode/)
+    .macOS(.v14), // Constrained by Swift 5.10 support for Xcode (https://developer.apple.com/support/xcode/)
 ]
-#endif

Package.swift

@@ -79,7 +79,7 @@ The PNNS implementation in Swift Homomorphic Encryption uses homomorphic encrypt
 Swift Homomorphic Encryption requires:
 * 64-bit processor with little-endian memory representation
 * macOS or Linux operating system
-* [Swift](https://www.swift.org/) version 6.0 or later
+* [Swift](https://www.swift.org/) version 5.10 or later
 
 > [!NOTE]
 > Swift Homomorphic Encryption relies on [SystemRandomNumberGenerator](https://developer.apple.com/documentation/swift/systemrandomnumbergenerator) as a cryptographically secure random number generator, which may have platform-dependent behavior.
@@ -134,7 +134,7 @@ swift run -c release EncryptionParametersSnippet
 ## Developing Swift Homomorphic Encryption
 ### Dependencies
 Building Swift Homomorphic Encryption requires:
-* [Swift](https://www.swift.org/) version 6.0 or later
+* [Swift](https://www.swift.org/) version 5.10 or later
 
 Additionally, developing Swift Homomorphic Encryption requires:
 * [Nick Lockwood SwiftFormat](https://github.com/nicklockwood/SwiftFormat), v0.54.0

README.md

@@ -717,5 +717,6 @@ extension DoubleWidthUInt: UnsignedInteger where Base: FixedWidthInteger & Unsig
     }
 }
 
+@usableFromInline typealias DWUInt128 = DoubleWidthUInt<UInt64>
 @usableFromInline typealias QuadWidth<T: FixedWidthInteger & UnsignedInteger> = DoubleWidthUInt<DoubleWidthUInt<T>>
 @usableFromInline typealias OctoWidth<T: FixedWidthInteger & UnsignedInteger> = DoubleWidthUInt<QuadWidth<T>>

Sources/HomomorphicEncryption/DoubleWidthUInt.swift

@@ -6,7 +6,7 @@ Get started using Swift Homomorphic Encryption.
 Swift Homomorphic Encryption requires:
 * 64-bit processor with little-endian memory representation
 * macOS or Linux operating system
-* [Swift](https://www.swift.org/) version 6.0 or later
+* [Swift](https://www.swift.org/) version 5.10 or later
 
 > Note: Swift Homomorphic Encryption relies on [SystemRandomNumberGenerator](https://developer.apple.com/documentation/swift/systemrandomnumbergenerator) as a cryptographically secure random number generator, which may have platform-dependent behavior.
 

Sources/HomomorphicEncryption/HomomorphicEncryption.docc/UsingSwiftHomomorphicEncryption.md

@@ -53,7 +53,7 @@ extension PolyRq {
     @inlinable
     public mutating func randomizeUniform(using rng: inout some PseudoRandomNumberGenerator) {
         let chunkCount = min(degree, 1024)
-        let uint128ByteCount = MemoryLayout<UInt128>.size
+        let uint128ByteCount = MemoryLayout<DWUInt128>.size
         var randomBytes: [UInt8] = .init(repeating: 0, count: chunkCount * uint128ByteCount)
         // We can sample directly in Coeff or Eval domain
         for (rnsIndex, reduceModulus) in context.reduceModuliUInt64.enumerated() {
@@ -63,7 +63,7 @@ extension PolyRq {
                 for index in 0..<chunkCount {
                     // NOTE: for interoperability always ask rng for a UInt128 and reduces it
                     let u128 =
-                        UInt128(littleEndianBytes: randomBytes[index * uint128ByteCount..<(index + 1) *
+                        DWUInt128(littleEndianBytes: randomBytes[index * uint128ByteCount..<(index + 1) *
                                 uint128ByteCount])
                     let u64 = reduceModulus.reduce(u128)
                     self[offset + index] = T(u64)
@@ -92,7 +92,7 @@ extension PolyRq {
             // consumed for each coefficient.
             let u64: UInt64 = rng.next()
             let u32: UInt32 = rng.next()
-            let u128 = UInt128(u64) &<< 32 | UInt128(u32)
+            let u128 = DWUInt128(u64) &<< 32 | DWUInt128(u32)
 
             let val = T(reductionModulus.reduce(u128))
             for (index, modulus) in zip(rnsIndices(coeffIndex: coeffIndex), moduli) {

Sources/HomomorphicEncryption/PolyRq/PolyRq+Randomize.swift

@@ -24,23 +24,17 @@ import Foundation
 @usableFromInline
 package struct NistCtrDrbg {
     @usableFromInline static let ReseedInterval: Int64 = 1 << 48
-
     @usableFromInline static let MaxByteCountPerRequest: Int = 1 << 16
-
     /// Size of AES block.
     @usableFromInline static let BlockCount: Int = 16
-
     /// Size of AES key.
     @usableFromInline static let KeyCount: Int = 16
-
     /// Size of the seed.
     @usableFromInline static let SeedCount: Int = KeyCount + BlockCount
 
     @usableFromInline var key: SymmetricKey
-
     /// This is called `V` in the NIST specification.
-    @usableFromInline var nonce: UInt128
-
+    @usableFromInline var nonce: DWUInt128
     @usableFromInline var reseedCounter: Int64
 
     @usableFromInline var nonceBytes: [UInt8] {
@@ -76,7 +70,7 @@ package struct NistCtrDrbg {
 
         let zeroes = [UInt8](repeating: 0, count: requestedByteCount)
         let output = try AES._CTR.encrypt(zeroes, using: key, nonce: .init(nonceBytes: nonceBytes))
-        nonce &+= UInt128(requestedByteCount.dividingCeil(Self.BlockCount, variableTime: true))
+        nonce &+= DWUInt128(requestedByteCount.dividingCeil(Self.BlockCount, variableTime: true))
 
         let additionalInput = [UInt8](repeating: 0, count: Self.SeedCount)
         try ctrDrbgUpdate(providedData: additionalInput)

Sources/HomomorphicEncryption/Random/NistCtrDrbg.swift

@@ -108,7 +108,7 @@ extension UInt32: ScalarType {
 }
 
 extension UInt64: ScalarType {
-    public typealias DoubleWidth = UInt128
+    public typealias DoubleWidth = DoubleWidthUInt<UInt64>
     public typealias SignedScalar = Int64
 
     public static var rnsCorrectionFactor: UInt64 {
@@ -161,7 +161,7 @@ extension UInt64: DoubleWidthType {
     public typealias Scalar = UInt32
 }
 
-extension UInt128: DoubleWidthType {
+extension DWUInt128: DoubleWidthType {
     /// Single-width scalar, with bit-width half that of the ``DoubleWidthType``.
     public typealias Scalar = UInt64
 }

Sources/HomomorphicEncryption/Scalar.swift

@@ -25,6 +25,21 @@ extension Sequence where Element: Hashable {
     }
 }
 
+// https://github.com/swiftlang/swift-evolution/blob/main/proposals/0220-count-where.md
+// introduced in swift 6
+#if swift(<6.0)
+extension Sequence {
+    @inlinable
+    package func count(where predicate: (Element) throws -> Bool) rethrows -> Int {
+        var count = 0
+        for element in self where try predicate(element) {
+            count += 1
+        }
+        return count
+    }
+}
+#endif
+
 extension FixedWidthInteger {
     // not a constant time operation
     @inlinable