Merge pull request #1759 from spevans/pr_decimal_doublevalue_fix

Decimal: Fix .doubleValue to use _length to only index valid mantissa elements.

Author: millenomi

Foundation/Decimal.swift

@@ -201,20 +201,19 @@ extension Decimal {
 
 extension Decimal : Hashable, Comparable {
     internal var doubleValue: Double {
+        if _length == 0 {
+            if _isNegative == 1 {
+                return Double.nan
+            } else {
+                return 0
+            }
+        }
+
         var d = 0.0
-        if _length == 0 && _isNegative == 1 {
-            return Double.nan
+        for idx in stride(from: min(_length, 8), to: 0, by: -1) {
+            d = d * 65536 + Double(self[idx - 1])
         }
-        
-        d = d * 65536 + Double(_mantissa.7)
-        d = d * 65536 + Double(_mantissa.6)
-        d = d * 65536 + Double(_mantissa.5)
-        d = d * 65536 + Double(_mantissa.4)
-        d = d * 65536 + Double(_mantissa.3)
-        d = d * 65536 + Double(_mantissa.2)
-        d = d * 65536 + Double(_mantissa.1)
-        d = d * 65536 + Double(_mantissa.0)
-        
+
         if _exponent < 0 {
             for _ in _exponent..<0 {
                 d /= 10.0
@@ -226,9 +225,11 @@ extension Decimal : Hashable, Comparable {
         }
         return _isNegative != 0 ? -d : d
     }
+
     public var hashValue: Int {
         return Int(bitPattern: __CFHashDouble(doubleValue))
     }
+
     public static func ==(lhs: Decimal, rhs: Decimal) -> Bool {
         if lhs.isNaN {
             return rhs.isNaN

TestFoundation/TestDecimal.swift

@@ -31,6 +31,7 @@ class TestDecimal: XCTestCase {
             ("test_SimpleMultiplication", test_SimpleMultiplication),
             ("test_SmallerNumbers", test_SmallerNumbers),
             ("test_ZeroPower", test_ZeroPower),
+            ("test_doubleValue", test_doubleValue)
         ]
     }
 
@@ -712,4 +713,88 @@ class TestDecimal: XCTestCase {
         XCTAssertEqual(1, negativeSix.raising(toPower: 0))
     }
 
+    func test_doubleValue() {
+        XCTAssertEqual(NSDecimalNumber(decimal:Decimal(0)).doubleValue, 0)
+        XCTAssertEqual(NSDecimalNumber(decimal:Decimal(1)).doubleValue, 1)
+        XCTAssertEqual(NSDecimalNumber(decimal:Decimal(-1)).doubleValue, -1)
+        XCTAssertTrue(NSDecimalNumber(decimal:Decimal.nan).doubleValue.isNaN)
+        XCTAssertEqual(NSDecimalNumber(decimal:Decimal(UInt64.max)).doubleValue, Double(1.8446744073709552e+19))
+        XCTAssertEqual(NSDecimalNumber(decimal:Decimal(string: "1234567890123456789012345678901234567890")!).doubleValue, Double(1.2345678901234568e+39))
+
+        var d = Decimal()
+        d._mantissa.0 = 1
+        d._mantissa.1 = 2
+        d._mantissa.2 = 3
+        d._mantissa.3 = 4
+        d._mantissa.4 = 5
+        d._mantissa.5 = 6
+        d._mantissa.6 = 7
+        d._mantissa.7 = 8
+
+        XCTAssertEqual(NSDecimalNumber(decimal: d).doubleValue, 0)
+        XCTAssertEqual(d, Decimal(0))
+
+        d._length = 1
+        XCTAssertEqual(NSDecimalNumber(decimal: d).doubleValue, 1)
+        XCTAssertEqual(d, Decimal(1))
+
+        d._length = 2
+        XCTAssertEqual(NSDecimalNumber(decimal: d).doubleValue, 131073)
+        XCTAssertEqual(d, Decimal(131073))
+
+        d._length = 3
+        XCTAssertEqual(NSDecimalNumber(decimal: d).doubleValue, 12885032961)
+        XCTAssertEqual(d, Decimal(12885032961))
+
+        d._length = 4
+        XCTAssertEqual(NSDecimalNumber(decimal: d).doubleValue, 1125912791875585)
+        XCTAssertEqual(d, Decimal(1125912791875585))
+
+        d._length = 5
+        XCTAssertEqual(NSDecimalNumber(decimal: d).doubleValue, 9.223484628133963e+19)
+        XCTAssertEqual(d, Decimal(string: "92234846281339633665")!)
+
+        d._length = 6
+        XCTAssertEqual(NSDecimalNumber(decimal: d).doubleValue, 7.253647152534056e+24)
+        XCTAssertEqual(d, Decimal(string: "7253647152534056387870721")!)
+
+        d._length = 7
+        XCTAssertEqual(NSDecimalNumber(decimal: d).doubleValue, 5.546043912470029e+29)
+        XCTAssertEqual(d, Decimal(string: "554604391247002897211195523073")!)
+
+        d._length = 8
+        XCTAssertEqual(NSDecimalNumber(decimal: d).doubleValue, 4.153892947266987e+34)
+        XCTAssertEqual(d, Decimal(string: "41538929472669868031141181829283841")!)
+
+        // The result of the subtractions can leave values in the internal mantissa of a and b,
+        // although _length = 0 which is correct.
+        let x = Decimal(10.5)
+        let y = Decimal(9.0)
+        let z = Decimal(1.5)
+        let a = x - y - z
+        let b = x - z - y
+
+        XCTAssertEqual(x.description, "10.5")
+        XCTAssertEqual(y.description, "9")
+        XCTAssertEqual(z.description, "1.5")
+        XCTAssertEqual(a.description, "0")
+        XCTAssertEqual(b.description, "0")
+        XCTAssertEqual(NSDecimalNumber(decimal: x).doubleValue, 10.5)
+        XCTAssertEqual(NSDecimalNumber(decimal: y).doubleValue, 9.0)
+        XCTAssertEqual(NSDecimalNumber(decimal: z).doubleValue, 1.5)
+        XCTAssertEqual(NSDecimalNumber(decimal: a).doubleValue, 0.0)
+        XCTAssertEqual(NSDecimalNumber(decimal: b).doubleValue, 0.0)
+
+        let nf = NumberFormatter()
+        nf.locale = Locale(identifier: "en_US")
+        nf.numberStyle = .decimal
+        nf.minimumFractionDigits = 2
+        nf.maximumFractionDigits = 2
+
+        XCTAssertEqual(nf.string(from: NSDecimalNumber(decimal: x)), "10.50")
+        XCTAssertEqual(nf.string(from: NSDecimalNumber(decimal: y)), "9.00")
+        XCTAssertEqual(nf.string(from: NSDecimalNumber(decimal: z)), "1.50")
+        XCTAssertEqual(nf.string(from: NSDecimalNumber(decimal: a)), "0.00")
+        XCTAssertEqual(nf.string(from: NSDecimalNumber(decimal: b)), "0.00")
+    }
 }