Avoid bounds checks in array intersection loops

setutil.go

@@ -296,51 +296,48 @@ func localintersect2by2(
 	if (len(set1) == 0) || (len(set2) == 0) {
 		return 0
 	}
-	k1 := 0
-	k2 := 0
 	pos := 0
 	buffer = buffer[:cap(buffer)]
-	s1 := set1[k1]
-	s2 := set2[k2]
+	s1 := set1[0]
+	s2 := set2[0]
 mainwhile:
 	for {
 		if s2 < s1 {
 			for {
-				k2++
-				if k2 == len(set2) {
+				if len(set2) <= 1 {
 					break mainwhile
 				}
-				s2 = set2[k2]
+				set2 = set2[1:]
+				s2 = set2[0]
 				if s2 >= s1 {
 					break
 				}
 			}
 		}
 		if s1 < s2 {
 			for {
-				k1++
-				if k1 == len(set1) {
+				if len(set1) <= 1 {
 					break mainwhile
 				}
-				s1 = set1[k1]
+				set1 = set1[1:]
+				s1 = set1[0]
 				if s1 >= s2 {
 					break
 				}
 			}
 		} else {
-			// (set2[k2] == set1[k1])
 			buffer[pos] = s1
 			pos++
-			k1++
-			if k1 == len(set1) {
+			if len(set1) <= 1 {
 				break
 			}
-			s1 = set1[k1]
-			k2++
-			if k2 == len(set2) {
+			set1 = set1[1:]
+			s1 = set1[0]
+			if len(set2) <= 1 {
 				break
 			}
-			s2 = set2[k2]
+			set2 = set2[1:]
+			s2 = set2[0]
 		}
 	}
 	return pos
@@ -354,49 +351,46 @@ func localintersect2by2Cardinality(
 	if (len(set1) == 0) || (len(set2) == 0) {
 		return 0
 	}
-	index1 := 0
-	index2 := 0
 	pos := 0
-	value1 := set1[index1]
-	value2 := set2[index2]
+	value1 := set1[0]
+	value2 := set2[0]
 mainwhile:
 	for {
 		if value2 < value1 {
 			for {
-				index2++
-				if index2 == len(set2) {
+				if len(set2) <= 1 {
 					break mainwhile
 				}
-				value2 = set2[index2]
+				set2 = set2[1:]
+				value2 = set2[0]
 				if value2 >= value1 {
 					break
 				}
 			}
 		}
 		if value1 < value2 {
 			for {
-				index1++
-				if index1 == len(set1) {
+				if len(set1) <= 1 {
 					break mainwhile
 				}
-				value1 = set1[index1]
+				set1 = set1[1:]
+				value1 = set1[0]
 				if value1 >= value2 {
 					break
 				}
 			}
 		} else {
-			// (set2[k2] == set1[k1])
 			pos++
-			index1++
-			if index1 == len(set1) {
+			if len(set1) <= 1 {
 				break
 			}
-			value1 = set1[index1]
-			index2++
-			if index2 == len(set2) {
+			set1 = set1[1:]
+			value1 = set1[0]
+			if len(set2) <= 1 {
 				break
 			}
-			value2 = set2[index2]
+			set2 = set2[1:]
+			value2 = set2[0]
 		}
 	}
 	return pos

setutil_test.go

@@ -390,3 +390,42 @@ func TestSetUtilUnionBy2Cardinality(t *testing.T) {
 		})
 	}
 }
+
+func arrayIntersectionBenchmarkBitmaps() (*Bitmap, *Bitmap) {
+	left := New()
+	right := New()
+	for high := uint32(0); high < 4; high++ {
+		base := high << 16
+		for low := uint32(0); low < 2*arrayDefaultMaxSize; low += 4 {
+			left.Add(base + low)
+			left.Add(base + low + 2)
+			right.Add(base + low)
+			right.Add(base + low + 1)
+		}
+	}
+	return left, right
+}
+
+func BenchmarkArrayIntersection(b *testing.B) {
+	left, right := arrayIntersectionBenchmarkBitmaps()
+	var result *Bitmap
+	b.ReportAllocs()
+	for b.Loop() {
+		result = And(left, right)
+	}
+	if got, want := result.GetCardinality(), uint64(4*arrayDefaultMaxSize/2); got != want {
+		b.Fatalf("unexpected intersection cardinality: got %d, want %d", got, want)
+	}
+}
+
+func BenchmarkArrayIntersectionCardinality(b *testing.B) {
+	left, right := arrayIntersectionBenchmarkBitmaps()
+	var result uint64
+	b.ReportAllocs()
+	for b.Loop() {
+		result = left.AndCardinality(right)
+	}
+	if want := uint64(4 * arrayDefaultMaxSize / 2); result != want {
+		b.Fatalf("unexpected intersection cardinality: got %d, want %d", result, want)
+	}
+}