Partially fix Decimal.ulp to return a valid representation.

Author: xwu

Darwin/Foundation-swiftoverlay-Tests/TestDecimal.swift

@@ -209,7 +209,7 @@ class TestDecimal : XCTestCase {
 
         let ulp = explicit.ulp
         XCTAssertEqual(0x7f, ulp.exponent)
-        XCTAssertEqual(8, ulp._length)
+        XCTAssertEqual(1, ulp._length)
         XCTAssertEqual(0, ulp._isNegative)
         XCTAssertEqual(1, ulp._isCompact)
         XCTAssertEqual(0, ulp._reserved)
@@ -588,6 +588,11 @@ class TestDecimal : XCTestCase {
             }
         }
     }
+    
+    func test_ULP() {
+        let x = 0.1 as Decimal
+        XCTAssertFalse(x.ulp > x)
+    }
 
     func test_unconditionallyBridgeFromObjectiveC() {
         XCTAssertEqual(Decimal(), Decimal._unconditionallyBridgeFromObjectiveC(nil))

Darwin/Foundation-swiftoverlay/Decimal.swift

@@ -503,7 +503,7 @@ extension Decimal {
     public var ulp: Decimal {
         if !self.isFinite { return Decimal.nan }
         return Decimal(
-            _exponent: _exponent, _length: 8, _isNegative: 0, _isCompact: 1,
+            _exponent: _exponent, _length: 1, _isNegative: 0, _isCompact: 1,
             _reserved: 0, _mantissa: (0x0001, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000))
     }
 

Sources/Foundation/Decimal.swift

@@ -731,7 +731,7 @@ extension Decimal {
     public var ulp: Decimal {
         if !self.isFinite { return Decimal.nan }
         return Decimal(
-            _exponent: _exponent, _length: 8, _isNegative: 0, _isCompact: 1,
+            _exponent: _exponent, _length: 1, _isNegative: 0, _isCompact: 1,
             _reserved: 0, _mantissa: (0x0001, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000))
     }
 

Tests/Foundation/Tests/TestDecimal.swift

@@ -271,7 +271,7 @@ class TestDecimal: XCTestCase {
 
         let ulp = explicit.ulp
         XCTAssertEqual(0x7f, ulp.exponent)
-        XCTAssertEqual(8, ulp._length)
+        XCTAssertEqual(1, ulp._length)
         XCTAssertEqual(0, ulp._isNegative)
         XCTAssertEqual(1, ulp._isCompact)
         XCTAssertEqual(0, ulp._reserved)
@@ -824,6 +824,11 @@ class TestDecimal: XCTestCase {
 
         XCTAssertEqual(100,number.objCType.pointee, "ObjC type for NSDecimalNumber is 'd'")
     }
+    
+    func test_ULP() {
+        let x = 0.1 as Decimal
+        XCTAssertFalse(x.ulp > x)
+    }
 
     func test_ZeroPower() {
         let six = NSDecimalNumber(integerLiteral: 6)
@@ -1430,6 +1435,7 @@ class TestDecimal: XCTestCase {
             ("test_ScanDecimal", test_ScanDecimal),
             ("test_SimpleMultiplication", test_SimpleMultiplication),
             ("test_SmallerNumbers", test_SmallerNumbers),
+            ("test_ULP", test_ULP),
             ("test_ZeroPower", test_ZeroPower),
             ("test_parseDouble", test_parseDouble),
             ("test_doubleValue", test_doubleValue),