p2p/enode: optimize DistCmp (#32888)

This speeds up DistCmp by 75% through using 64-bit operations instead of
byte-wise XOR.

Author: cuiweixie

p2p/enode/node.go

@@ -359,9 +359,10 @@ func ParseID(in string) (ID, error) {
 // Returns -1 if a is closer to target, 1 if b is closer to target
 // and 0 if they are equal.
 func DistCmp(target, a, b ID) int {
-	for i := range target {
-		da := a[i] ^ target[i]
-		db := b[i] ^ target[i]
+	for i := 0; i < len(target); i += 8 {
+		tn := binary.BigEndian.Uint64(target[i : i+8])
+		da := tn ^ binary.BigEndian.Uint64(a[i:i+8])
+		db := tn ^ binary.BigEndian.Uint64(b[i:i+8])
 		if da > db {
 			return 1
 		} else if da < db {

p2p/enode/node_test.go

@@ -368,6 +368,16 @@ func TestID_distcmpEqual(t *testing.T) {
 	}
 }
 
+func BenchmarkDistCmp(b *testing.B) {
+	base := ID{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15}
+	aID := ID{15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0}
+	bID := ID{15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 1}
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = DistCmp(base, aID, bID)
+	}
+}
+
 func TestID_logdist(t *testing.T) {
 	logdistBig := func(a, b ID) int {
 		abig, bbig := new(big.Int).SetBytes(a[:]), new(big.Int).SetBytes(b[:])