dht: Reduce allocations in calculating ID distance

diff --git a/dht/dht.go b/dht/dht.go
index 010489fc895ccae80d1115670740165bf6c6a658..71ae1cf7e7de90b21a23afc64f6406449d5521d9 100644 (file)
--- a/dht/dht.go
+++ b/dht/dht.go
@@ -912,7 +912,7 @@ type distance interface {
 }
 
 type bigIntDistance struct {
-       *big.Int
+       big.Int
 }
 
 // How many bits?
@@ -962,15 +962,16 @@ var bitCounts = []int8{
 }
 
 func (me bigIntDistance) BitCount() int {
-       return bitCount(me.Int)
+       return bitCount(&me.Int)
 }
 
-func (me bigIntDistance) Cmp(d distance) int {
-       return me.Int.Cmp(d.(bigIntDistance).Int)
+func (me bigIntDistance) Cmp(d bigIntDistance) int {
+       return me.Int.Cmp(&d.Int)
 }
 
 func (me bigIntDistance) IsZero() bool {
-       return me.Int.Cmp(big.NewInt(0)) == 0
+       var zero big.Int
+       return me.Int.Cmp(&zero) == 0
 }
 
 type bitCountDistance int
@@ -992,31 +993,32 @@ func (me bitCountDistance) IsZero() bool {
        return me == 0
 }
 
-func idDistance(a, b string) distance {
-       if true {
-               if len(a) != 20 {
-                       panic(a)
-               }
-               if len(b) != 20 {
-                       panic(b)
-               }
-               x := new(big.Int)
-               y := new(big.Int)
-               x.SetBytes([]byte(a))
-               y.SetBytes([]byte(b))
-               dist := new(big.Int)
-               return bigIntDistance{dist.Xor(x, y)}
-       } else {
-               ret := 0
-               for i := 0; i < 20; i++ {
-                       for j := uint(0); j < 8; j++ {
-                               ret += int(a[i]>>j&1 ^ b[i]>>j&1)
-                       }
-               }
-               return bitCountDistance(ret)
+// Below are 2 versions of idDistance. Only one can be active.
+
+func idDistance(a, b string) (ret bigIntDistance) {
+       if len(a) != 20 {
+               panic(a)
+       }
+       if len(b) != 20 {
+               panic(b)
        }
+       var x, y big.Int
+       x.SetBytes([]byte(a))
+       y.SetBytes([]byte(b))
+       ret.Int.Xor(&x, &y)
+       return ret
 }
 
+// func idDistance(a, b string) bitCountDistance {
+//     ret := 0
+//     for i := 0; i < 20; i++ {
+//             for j := uint(0); j < 8; j++ {
+//                     ret += int(a[i]>>j&1 ^ b[i]>>j&1)
+//             }
+//     }
+//     return bitCountDistance(ret)
+// }
+
 func (s *Server) closestGoodNodes(k int, targetID string) []*Node {
        return s.closestNodes(k, targetID, func(n *Node) bool { return n.Good() })
 }