#33 optimize XPath union operation(|) performance, 1000x times faster

antchfx/htmlquery#10

query.go

@@ -1,6 +1,9 @@
 package xpath
 
 import (
+	"bytes"
+	"fmt"
+	"hash/fnv"
 	"reflect"
 )
 
@@ -728,35 +731,36 @@ type unionQuery struct {
 
 func (u *unionQuery) Select(t iterator) NodeNavigator {
 	if u.iterator == nil {
-		var list []NodeNavigator
-		var i int
+		var m = make(map[uint64]NodeNavigator)
 		root := t.Current().Copy()
 		for {
 			node := u.Left.Select(t)
 			if node == nil {
 				break
 			}
-			node = node.Copy()
-			list = append(list, node)
+			code := getHashCode(node.Copy())
+			if _, ok := m[code]; !ok {
+				m[code] = node.Copy()
+			}
 		}
 		t.Current().MoveTo(root)
 		for {
 			node := u.Right.Select(t)
 			if node == nil {
 				break
 			}
-			node = node.Copy()
-			var exists bool
-			for _, x := range list {
-				if reflect.DeepEqual(x, node) {
-					exists = true
-					break
-				}
-			}
-			if !exists {
-				list = append(list, node)
+			code := getHashCode(node.Copy())
+			if _, ok := m[code]; !ok {
+				m[code] = node.Copy()
 			}
 		}
+		list := make([]NodeNavigator, len(m))
+		var i int
+		for _, v := range m {
+			list[i] = v
+			i++
+		}
+		i = 0
 		u.iterator = func() NodeNavigator {
 			if i >= len(list) {
 				return nil
@@ -780,6 +784,35 @@ func (u *unionQuery) Clone() query {
 	return &unionQuery{Left: u.Left.Clone(), Right: u.Right.Clone()}
 }
 
+func getHashCode(n NodeNavigator) uint64 {
+	var sb bytes.Buffer
+	switch n.NodeType() {
+	case AttributeNode, TextNode, CommentNode:
+		sb.WriteString(fmt.Sprintf("%s=%s", n.LocalName(), n.Value()))
+		if n.MoveToParent() {
+			sb.WriteString(n.LocalName())
+		}
+	case ElementNode:
+		sb.WriteString(n.Prefix() + n.LocalName())
+		d := 1
+		for n.MoveToPrevious() {
+			d++
+		}
+		sb.WriteString(fmt.Sprintf("-%d", d))
+
+		for n.MoveToParent() {
+			d = 1
+			for n.MoveToPrevious() {
+				d++
+			}
+			sb.WriteString(fmt.Sprintf("-%d", d))
+		}
+	}
+	h := fnv.New64a()
+	h.Write([]byte(sb.String()))
+	return h.Sum64()
+}
+
 func getNodePosition(q query) int {
 	type Position interface {
 		position() int