Merge pull request #3486 from xwu/SR-1818

Fix IndexSet intersection and symmetric difference [SR-1818]

Author: parkera

stdlib/public/SDK/Foundation/IndexSet.swift

@@ -551,21 +551,19 @@ public struct IndexSet : ReferenceConvertible, Equatable, BidirectionalCollectio
 
         while let i = boundaryIterator.next() {
             if !flag {
-                // Starting a range; if the edge is contained or not depends on the xor of this particular value.
-                let startInclusive = self.contains(i) != other.contains(i)
-                start = startInclusive ? i : i + 1
-                flag = true
+                // Start a range if one set contains but not the other.
+                if self.contains(i) != other.contains(i) {
+                    flag = true
+                    start = i
+                }
             } else {
-                // Ending a range; if the edge is contained or not depends on the xor of this particular value.
-                let endInclusive = self.contains(i) != other.contains(i)
-                let end = endInclusive ? i + 1 : i
-                if start < end {
-                    // Otherwise, we had an empty range
-                    result.insert(integersIn: start..<end)
+                // End a range if both sets contain or both sets do not contain.
+                if self.contains(i) == other.contains(i) {
+                    flag = false
+                    result.insert(integersIn: start..<i)
                 }
-                flag = false
             }
-            // We never have to worry about having flag set to false after exiting this loop because the iterator will always return an even number of results; ranges come in pairs, and we always alternate flag
+            // We never have to worry about having flag set to false after exiting this loop because the last boundary is guaranteed to be past the end of ranges in both index sets
         }
 
         return result
@@ -591,10 +589,10 @@ public struct IndexSet : ReferenceConvertible, Equatable, BidirectionalCollectio
                     start = i
                 }
             } else {
-                // If both sets contain then end a range.
-                if self.contains(i) && other.contains(i) {
+                // If both sets do not contain then end a range.
+                if !self.contains(i) || !other.contains(i) {
                     flag = false
-                    result.insert(integersIn: start..<(i + 1))
+                    result.insert(integersIn: start..<i)
                 }
             }
         }
@@ -783,8 +781,8 @@ private struct IndexSetBoundaryIterator : IteratorProtocol {
     private var i2 : IndexSet.RangeView.Iterator
     private var i1Range : CountableRange<Element>?
     private var i2Range : CountableRange<Element>?
-    private var i1UsedFirst : Bool
-    private var i2UsedFirst : Bool
+    private var i1UsedLower : Bool
+    private var i2UsedLower : Bool
 
     private init(_ is1 : IndexSet, _ is2 : IndexSet) {
         i1 = is1.rangeView.makeIterator()
@@ -793,9 +791,9 @@ private struct IndexSetBoundaryIterator : IteratorProtocol {
         i1Range = i1.next()
         i2Range = i2.next()
 
-        // A sort of cheap iterator on [i1Range.first, i1Range.last]
-        i1UsedFirst = false
-        i2UsedFirst = false
+        // A sort of cheap iterator on [i1Range.lowerBound, i1Range.upperBound]
+        i1UsedLower = false
+        i2UsedLower = false
     }
 
     private mutating func next() -> Element? {
@@ -805,29 +803,34 @@ private struct IndexSetBoundaryIterator : IteratorProtocol {
 
         let nextIn1 : Element
         if let r = i1Range {
-            nextIn1 = i1UsedFirst ? r.last! : r.first!
+            nextIn1 = i1UsedLower ? r.upperBound : r.lowerBound
         } else {
             nextIn1 = Int.max
         }
 
         let nextIn2 : Element
         if let r = i2Range {
-            nextIn2 = i2UsedFirst ? r.last! : r.first!
+            nextIn2 = i2UsedLower ? r.upperBound : r.lowerBound
         } else {
             nextIn2 = Int.max
         }
 
         var result : Element
         if nextIn1 <= nextIn2 {
-            // 1 has the next element, or they are the same. We need to iterate both the value from is1 and is2 in the == case.
+            // 1 has the next element, or they are the same.
             result = nextIn1
-            if i1UsedFirst { i1Range = i1.next() }
-            i1UsedFirst = !i1UsedFirst
+            if i1UsedLower { i1Range = i1.next() }
+            // We need to iterate both the value from is1 and is2 in the == case.
+            if result == nextIn2 {
+                if i2UsedLower { i2Range = i2.next() }
+                i2UsedLower = !i2UsedLower
+            }
+            i1UsedLower = !i1UsedLower
         } else {
             // 2 has the next element
             result = nextIn2
-            if i2UsedFirst { i2Range = i2.next() }
-            i2UsedFirst = !i2UsedFirst
+            if i2UsedLower { i2Range = i2.next() }
+            i2UsedLower = !i2UsedLower
         }
 
         return result

test/1_stdlib/TestIndexSet.swift

@@ -516,6 +516,12 @@ class TestIndexSet : TestIndexSetSuper {
             expectEqual(expected, is1.symmetricDifference(is2))
             expectEqual(expected, is2.symmetricDifference(is1))
         }
+        
+        do {
+            is1 = IndexSet([0, 2])
+            is2 = IndexSet([0, 1, 2])
+            expectEqual(IndexSet(integer: 1), is1.symmetricDifference(is2))
+        }
     }
 
     func testIntersection() {
@@ -587,7 +593,12 @@ class TestIndexSet : TestIndexSetSuper {
             expectEqual(expected, is1.intersection(is2))
             expectEqual(expected, is2.intersection(is1))
         }
-
+        
+        do {
+            is1 = IndexSet([0, 2])
+            is2 = IndexSet([0, 1, 2])
+            expectEqual(is1, is1.intersection(is2))
+        }
     }
 
     func testUnion() {