From 3e8030aee427e3de837431a54156919865bf7047 Mon Sep 17 00:00:00 2001
From: Matt Jaffee <jaffee@umbel.com>
Date: Fri, 19 May 2017 08:22:56 -0500
Subject: [PATCH] implement intersectRunRun

---
 roaring/roaring.go               | 35 +++++++++++++++++++++++++++++++-
 roaring/roaring_internal_test.go | 35 ++++++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+), 1 deletion(-)

diff --git a/roaring/roaring.go b/roaring/roaring.go
index 1d8ef1223..516a76f5e 100644
--- a/roaring/roaring.go
+++ b/roaring/roaring.go
@@ -1645,6 +1645,9 @@ func intersectArrayArray(a, b *container) *container {
 	return output
 }
 
+// intersectArrayRun computes the intersect of an array container and a run
+// container. The return is always an array container (since it's guaranteed to
+// be low-cardinality)
 func intersectArrayRun(a, b *container) *container {
 	output := &container{}
 	na, nb := len(a.array), len(b.runs)
@@ -1663,9 +1666,39 @@ func intersectArrayRun(a, b *container) *container {
 	return output
 }
 
+// intersectRunRun computes the intersect of two run containers. The output is
+// always a run container, since it can't possible have more runs than either of
+// the inputs. (note: it is possible that an array container would be better in
+// some cases, but probably not worth complicating the implementation)
 func intersectRunRun(a, b *container) *container {
 	output := &container{}
-	// TODO
+	na, nb := len(a.runs), len(b.runs)
+	for i, j := 0, 0; i < na && j < nb; {
+		va, vb := a.runs[i], b.runs[j]
+		if va.last < vb.start {
+			// |--va--| |--vb--|
+			i++
+		} else if vb.last < va.start {
+			// |--vb--| |--va--|
+			j++
+		} else if va.last > vb.last && va.start >= vb.start {
+			// |--vb-|-|-va--|
+			output.runs = append(output.runs, interval32{start: va.start, last: vb.last})
+			j++
+		} else if va.last > vb.last && va.start < vb.start {
+			// |--va|--vb--|--|
+			output.runs = append(output.runs, vb)
+			j++
+		} else if va.last <= vb.last && va.start >= vb.start {
+			// |--vb|--va--|--|
+			output.runs = append(output.runs, va)
+			i++
+		} else if va.last <= vb.last && va.start < vb.start {
+			// |--va-|-|-vb--|
+			output.runs = append(output.runs, interval32{start: vb.start, last: va.last})
+			i++
+		}
+	}
 	return output
 }
 
diff --git a/roaring/roaring_internal_test.go b/roaring/roaring_internal_test.go
index 8f771a1fe..c250d57d7 100644
--- a/roaring/roaring_internal_test.go
+++ b/roaring/roaring_internal_test.go
@@ -390,3 +390,38 @@ func TestIntersectArrayRun(t *testing.T) {
 		}
 	}
 }
+
+func TestIntersectRunRun(t *testing.T) {
+	a := &container{}
+	b := &container{}
+	tests := []struct {
+		aruns []interval32
+		bruns []interval32
+		exp   []interval32
+	}{
+		{
+			aruns: []interval32{},
+			bruns: []interval32{{start: 5, last: 10}},
+			exp:   []interval32(nil),
+		},
+		{
+			aruns: []interval32{{start: 5, last: 12}},
+			bruns: []interval32{{start: 5, last: 10}},
+			exp:   []interval32{{start: 5, last: 10}},
+		},
+		{
+			aruns: []interval32{{start: 1, last: 3}, {start: 5, last: 5}, {start: 7, last: 8}, {start: 9, last: 12}},
+			bruns: []interval32{{start: 5, last: 10}},
+			exp:   []interval32{{start: 5, last: 5}, {start: 7, last: 8}, {start: 9, last: 10}},
+		},
+	}
+	for i, test := range tests {
+		a.runs = test.aruns
+		b.runs = test.bruns
+		ret := intersectRunRun(a, b)
+		if !reflect.DeepEqual(ret.runs, test.exp) {
+			t.Fatalf("test #%v expected %v, but got %v", i, test.exp, ret.runs)
+		}
+	}
+
+}