[SR-15156] Another fix for Decimal(sign:exponent:significand:).

Author: xwu

Darwin/Foundation-swiftoverlay-Tests/TestDecimal.swift

@@ -580,8 +580,10 @@ class TestDecimal : XCTestCase {
 
         let a = Decimal.leastNonzeroMagnitude
         XCTAssertEqual(Decimal(sign: .plus, exponent: -10, significand: a), 0)
+        XCTAssertEqual(Decimal(sign: .plus, exponent: .min, significand: a), 0)
         let b = Decimal.greatestFiniteMagnitude
         XCTAssertTrue(Decimal(sign: .plus, exponent: 10, significand: b).isNaN)
+        XCTAssertTrue(Decimal(sign: .plus, exponent: .max, significand: b).isNaN)
     }
 
     func test_SimpleMultiplication() {

Darwin/Foundation-swiftoverlay/Decimal.swift

@@ -519,7 +519,7 @@ extension Decimal {
     public init(sign: FloatingPointSign, exponent: Int, significand: Decimal) {
         self = significand
         let error = withUnsafeMutablePointer(to: &self) {
-            NSDecimalMultiplyByPowerOf10($0, $0, Int16(exponent), .plain)
+            NSDecimalMultiplyByPowerOf10($0, $0, Int16(clamping: exponent), .plain)
         }
         if error == .underflow { self = 0 }
         // We don't need to check for overflow because `Decimal` cannot represent infinity.

Sources/Foundation/Decimal.swift

@@ -687,7 +687,7 @@ extension Decimal {
     public init(sign: FloatingPointSign, exponent: Int, significand: Decimal) {
         self = significand
         let error = withUnsafeMutablePointer(to: &self) {
-            NSDecimalMultiplyByPowerOf10($0, $0, Int16(exponent), .plain)
+            NSDecimalMultiplyByPowerOf10($0, $0, Int16(clamping: exponent), .plain)
         }
         if error == .underflow { self = 0 }
         // We don't need to check for overflow because `Decimal` cannot represent infinity.

Tests/Foundation/Tests/TestDecimal.swift

@@ -821,8 +821,10 @@ class TestDecimal: XCTestCase {
 
         let a = Decimal.leastNonzeroMagnitude
         XCTAssertEqual(Decimal(sign: .plus, exponent: -10, significand: a), 0)
+        XCTAssertEqual(Decimal(sign: .plus, exponent: .min, significand: a), 0)
         let b = Decimal.greatestFiniteMagnitude
         XCTAssertTrue(Decimal(sign: .plus, exponent: 10, significand: b).isNaN)
+        XCTAssertTrue(Decimal(sign: .plus, exponent: .max, significand: b).isNaN)
     }
 
     func test_SimpleMultiplication() {