Merge pull request #949 from tgruben/range-bug

fix overflow in differenceRunBitmap

roaring/roaring.go

@@ -2508,17 +2508,25 @@ func differenceRunArray(a, b *container) *container {
 // differenceRunBitmap computes the difference of an run from a bitmap.
 func differenceRunBitmap(a, b *container) *container {
 	// If a is full, difference is the flip of b.
-	if a.runs[0].start == 0 && a.runs[0].last == 65535 {
+	if len(a.runs) > 0 && a.runs[0].start == 0 && a.runs[0].last == 65535 {
 		return b.flipBitmap()
 	}
 	output := &container{container_type: ContainerRun}
 	output.n = a.n
+	if len(a.runs) == 0 {
+		return output
+	}
 	for j := 0; j < len(a.runs); j++ {
 		run := a.runs[j]
+		add := true
 		for bit := a.runs[j].start; bit <= a.runs[j].last; bit++ {
 			if b.bitmapContains(bit) {
 				output.n--
 				if run.start == bit {
+					if bit == 65535 { //overflow
+						add = false
+					}
+
 					run.start++
 				} else if bit == run.last {
 					run.last--
@@ -2534,10 +2542,15 @@ func differenceRunBitmap(a, b *container) *container {
 					break
 				}
 			}
+
+			if bit == 65535 { //overflow
+				break
+			}
 		}
 		if run.start <= run.last {
-			output.runs = append(output.runs, run)
-
+			if add {
+				output.runs = append(output.runs, run)
+			}
 		}
 	}
 

roaring/roaring_internal_test.go

@@ -1485,6 +1485,12 @@ func MakeBitmap(start []uint64) []uint64 {
 	}
 	return b
 }
+func MakeLastBitSet() []uint64 {
+	obj := NewBitmap(65535)
+	c := obj.container(0)
+	c.arrayToBitmap()
+	return c.bitmap
+}
 
 func TestDifferenceRunBitmap(t *testing.T) {
 	a := &container{}
@@ -1524,14 +1530,24 @@ func TestDifferenceRunBitmap(t *testing.T) {
 			bitmap: MakeBitmap([]uint64{0x0, 0x8000000000000000}),
 			exp:    []interval16{{start: 0, last: 65}},
 		},
+		{
+			runs:   []interval16{{start: 1, last: 65535}},
+			bitmap: MakeBitmap([]uint64{0x0000000000000001}),
+			exp:    []interval16{{start: 1, last: 65535}},
+		},
+		{
+			runs:   []interval16{{start: 0, last: 65533}, {start: 65535, last: 65535}},
+			bitmap: MakeLastBitSet(),
+			exp:    []interval16{{start: 0, last: 65533}},
+		},
 	}
 	for i, test := range tests {
 		a.runs = test.runs
-		a.n = a.runCountRange(0, 100)
+		a.n = a.runCountRange(0, 65536)
 		for i, v := range test.bitmap {
 			b.bitmap[i] = v
 		}
-		b.n = b.bitmapCountRange(0, 100)
+		b.n = b.bitmapCountRange(0, 65536)
 		ret := differenceRunBitmap(a, b)
 		if !reflect.DeepEqual(ret.runs, test.exp) {
 			t.Fatalf("test #%v expected %v, but got %v", i, test.exp, ret.runs)