[BigInt tests] ✅🐰 Codable

Tests/BigIntTests/CodableTests.swift

@@ -0,0 +1,72 @@
+//===--- CodableTests.swift -----------------------------------*- swift -*-===//
+//
+// This source file is part of the Swift Numerics open source project
+//
+// Copyright (c) 2023 Apple Inc. and the Swift Numerics project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+//
+//===----------------------------------------------------------------------===//
+
+import XCTest
+@testable import BigIntModule
+
+// The only property that we care about is that `encode -> decode` works.
+// The transport format does not matter.
+// Though as soon as we commit to 1 representation we have to keep it forever.
+class CodableTests: XCTestCase {
+
+  func test_equalsString_radix10() {
+    let encoder = JSONEncoder()
+
+    for p in generateBigInts(approximateCount: 100) {
+      let big = p.create()
+
+      do {
+        let data = try encoder.encode(big)
+        let json = String(bytes: data, encoding: .utf8)
+        assert(json != nil)
+
+        let expected = "\"" + String(big, radix: 10) + "\""
+        XCTAssertEqual(json, expected)
+      } catch {
+        XCTFail("\(big)")
+      }
+    }
+  }
+
+  func test_int() {
+    let encoder = JSONEncoder()
+    let decoder = JSONDecoder()
+
+    for int in generateInts(approximateCount: 1000) {
+      let big = BigInt(int)
+
+      do {
+        let data = try encoder.encode(big)
+        let restored = try decoder.decode(BigInt.self, from: data)
+        XCTAssertEqual(big, restored)
+      } catch {
+        XCTFail("\(int)")
+      }
+    }
+  }
+
+  func test_big() {
+    let encoder = JSONEncoder()
+    let decoder = JSONDecoder()
+
+    for p in generateBigInts(approximateCount: 1000) {
+      let big = p.create()
+
+      do {
+        let data = try encoder.encode(big)
+        let restored = try decoder.decode(BigInt.self, from: data)
+        XCTAssertEqual(big, restored)
+      } catch {
+        XCTFail("\(big)")
+      }
+    }
+  }
+}

Tests/BigIntTests/Helpers/BigInt+Extensions.swift

@@ -0,0 +1,69 @@
+//===--- BigInt+Extensions.swift ------------------------------*- swift -*-===//
+//
+// This source file is part of the Swift Numerics open source project
+//
+// Copyright (c) 2023 Apple Inc. and the Swift Numerics project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+//
+//===----------------------------------------------------------------------===//
+
+import BigIntModule
+
+extension BigInt {
+
+  internal typealias Word = Words.Element
+
+  internal init(isPositive: Bool, magnitude: [BigIntPrototype.Word]) {
+    let p = BigIntPrototype(isPositive: isPositive, magnitude: magnitude)
+    self = p.create()
+  }
+
+  internal init(_ sign: BigIntPrototype.Sign, magnitude: BigIntPrototype.Word) {
+    let p = BigIntPrototype(sign, magnitude: magnitude)
+    self = p.create()
+  }
+
+  internal init(_ sign: BigIntPrototype.Sign, magnitude: [BigIntPrototype.Word]) {
+    let p = BigIntPrototype(sign, magnitude: magnitude)
+    self = p.create()
+  }
+
+  internal func power(exponent: BigInt) -> BigInt {
+    precondition(exponent >= 0, "Exponent must be positive")
+
+    if exponent == 0 {
+      return BigInt(1)
+    }
+
+    if exponent == 1 {
+      return self
+    }
+
+    // This has to be after 'exp == 0', because 'pow(0, 0) -> 1'
+    if self == 0 {
+      return 0
+    }
+
+    var base = self
+    var exponent = exponent
+    var result = BigInt(1)
+
+    // Eventually we will arrive to most significant '1'
+    while exponent != 1 {
+      let exponentIsOdd = exponent & 0b1 == 1
+
+      if exponentIsOdd {
+        result *= base
+      }
+
+      base *= base
+      exponent >>= 1 // Basically divided by 2, but faster
+    }
+
+    // Most significant '1' is odd:
+    result *= base
+    return result
+  }
+}