From 8fd752ddb14461896d03c210142742060ab68b20 Mon Sep 17 00:00:00 2001
From: Travis <travis@pilosa.com>
Date: Thu, 22 Jun 2017 16:01:52 -0500
Subject: [PATCH 1/2] bug fix in `differenceArrayRun` logic. add more test
 coverage for `differenceArrayRun`

---
 roaring/roaring.go      | 33 ++++++++++++++++++++-------------
 roaring/roaring_test.go | 28 ++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 13 deletions(-)

diff --git a/roaring/roaring.go b/roaring/roaring.go
index 66ce116eb..653831940 100644
--- a/roaring/roaring.go
+++ b/roaring/roaring.go
@@ -453,7 +453,6 @@ func (b *Bitmap) Difference(other *Bitmap) *Bitmap {
 		}
 
 	}
-
 	return output
 }
 
@@ -2488,29 +2487,37 @@ func differenceArrayRun(a, b *container) *container {
 	i := 0 // array index
 	j := 0 // run index
 
-	// keep all array elements before beginning of runs
-	for ; i < len(a.array) && a.array[i] < b.runs[j].start; i++ {
-		output.array = append(output.array, a.array[i])
-	}
-
 	// handle overlap
-	for ; i < a.n; i++ {
-		// if array element in run, keep
-		if !(a.array[i] >= b.runs[j].start && a.array[i] <= b.runs[j].last) {
-			output.array = append(output.array, a.array[i])
+	for i < a.n {
+
+		// keep all array elements before beginning of runs
+		if a.array[i] < b.runs[j].start {
+			output.add(a.array[i])
+			i++
+			continue
 		}
-		// update current run
-		if a.array[i] >= b.runs[j].last {
+
+		// if array element in run, skip it
+		if a.array[i] >= b.runs[j].start && a.array[i] <= b.runs[j].last {
+			i++
+			continue
+		}
+
+		// if array element larger than current run, check next run
+		if a.array[i] > b.runs[j].last {
 			j++
 			if j == len(b.runs) {
 				break
 			}
 		}
 	}
-	i++
+
 	if i < len(a.array) {
 		// keep all array elements after end of runs
 		output.array = append(output.array, a.array[i:]...)
+		// TODO: consider handling container.n mutations in one place
+		// like we do with container.add().
+		output.n += len(a.array[i:])
 	}
 	return output
 }
diff --git a/roaring/roaring_test.go b/roaring/roaring_test.go
index a097e1fbe..fc0a48966 100644
--- a/roaring/roaring_test.go
+++ b/roaring/roaring_test.go
@@ -242,6 +242,7 @@ func TestBitmap_Difference(t *testing.T) {
 		t.Fatalf("unexpected n: %d", n)
 	}
 }
+
 func TestBitmap_Difference_Empty(t *testing.T) {
 	bm0 := roaring.NewBitmap(0, 2683177)
 	bm1 := roaring.NewBitmap()
@@ -251,6 +252,33 @@ func TestBitmap_Difference_Empty(t *testing.T) {
 	}
 }
 
+func TestBitmap_DifferenceArrayArray(t *testing.T) {
+	bm0 := roaring.NewBitmap(0, 4, 8, 12, 16, 20)
+	bm1 := roaring.NewBitmap(1, 3, 6, 9, 12, 15, 18)
+	result := bm0.Difference(bm1)
+	if n := result.Count(); n != 5 {
+		t.Fatalf("unexpected n: %d", n)
+	}
+}
+
+func TestBitmap_DifferenceArrayRun(t *testing.T) {
+	bm0 := roaring.NewBitmap(0, 4, 8, 12, 16, 20, 36, 40, 44)
+
+	bm1 := roaring.NewBitmap(1, 2, 3, 4, 5, 6, 7, 8, 9, 30, 31, 32, 33, 34, 35, 36)
+	bm1.Optimize() // convert to runs
+	result := bm0.Difference(bm1)
+	if n := result.Count(); n != 6 {
+		t.Fatalf("unexpected n: %d", n)
+	}
+
+	// ensure empty array returns empty
+	bm2 := roaring.NewBitmap()
+	result = bm2.Difference(bm1)
+	if n := result.Count(); n != 0 {
+		t.Fatalf("unexpected n: %d", n)
+	}
+}
+
 func TestBitmap_Union(t *testing.T) {
 	bm0 := roaring.NewBitmap(0, 1000001, 1000002, 1000003)
 	bm1 := roaring.NewBitmap(0, 50000, 1000001, 1000002)

From fc6898a9337b40432be1da1b23c14d4fd1037dae Mon Sep 17 00:00:00 2001
From: Travis <travis@pilosa.com>
Date: Thu, 22 Jun 2017 16:07:21 -0500
Subject: [PATCH 2/2] remove a test that was not testing the correct thing

---
 roaring/roaring_test.go | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/roaring/roaring_test.go b/roaring/roaring_test.go
index fc0a48966..98c789043 100644
--- a/roaring/roaring_test.go
+++ b/roaring/roaring_test.go
@@ -270,13 +270,6 @@ func TestBitmap_DifferenceArrayRun(t *testing.T) {
 	if n := result.Count(); n != 6 {
 		t.Fatalf("unexpected n: %d", n)
 	}
-
-	// ensure empty array returns empty
-	bm2 := roaring.NewBitmap()
-	result = bm2.Difference(bm1)
-	if n := result.Count(); n != 0 {
-		t.Fatalf("unexpected n: %d", n)
-	}
 }
 
 func TestBitmap_Union(t *testing.T) {