reduce the number of slice reallocations

Should make the DHT less CPU hungry.

sorting.go

@@ -25,6 +25,11 @@ func (p peerSorterArr) Less(a, b int) bool {
 //
 
 func copyPeersFromList(target ID, peerArr peerSorterArr, peerList *list.List) peerSorterArr {
+	if cap(peerArr) < len(peerArr)+peerList.Len() {
+		newArr := make(peerSorterArr, 0, len(peerArr)+peerList.Len())
+		copy(newArr, peerArr)
+		peerArr = newArr
+	}
 	for e := peerList.Front(); e != nil; e = e.Next() {
 		p := e.Value.(peer.ID)
 		pID := ConvertPeerID(p)
@@ -38,7 +43,7 @@ func copyPeersFromList(target ID, peerArr peerSorterArr, peerList *list.List) pe
 }
 
 func SortClosestPeers(peers []peer.ID, target ID) []peer.ID {
-	var psarr peerSorterArr
+	psarr := make(peerSorterArr, 0, len(peers))
 	for _, p := range peers {
 		pID := ConvertPeerID(p)
 		pd := &peerDistance{
@@ -48,7 +53,7 @@ func SortClosestPeers(peers []peer.ID, target ID) []peer.ID {
 		psarr = append(psarr, pd)
 	}
 	sort.Sort(psarr)
-	var out []peer.ID
+	out := make([]peer.ID, 0, len(psarr))
 	for _, p := range psarr {
 		out = append(out, p.p)
 	}

table.go

@@ -165,7 +165,7 @@ func (rt *RoutingTable) NearestPeers(id ID, count int) []peer.ID {
 	}
 	bucket = rt.Buckets[cpl]
 
-	var peerArr peerSorterArr
+	peerArr := make(peerSorterArr, 0, count)
 	peerArr = copyPeersFromList(id, peerArr, bucket.list)
 	if len(peerArr) < count {
 		// In the case of an unusual split, one bucket may be short or empty.
@@ -185,9 +185,13 @@ func (rt *RoutingTable) NearestPeers(id ID, count int) []peer.ID {
 	// Sort by distance to local peer
 	sort.Sort(peerArr)
 
-	var out []peer.ID
-	for i := 0; i < count && i < peerArr.Len(); i++ {
-		out = append(out, peerArr[i].p)
+	if count < len(peerArr) {
+		peerArr = peerArr[:count]
+	}
+
+	out := make([]peer.ID, 0, len(peerArr))
+	for _, p := range peerArr {
+		out = append(out, p.p)
 	}
 
 	return out