consensus/clique: replace bubble sort by golang stable sort

consensus/clique/snapshot.go

@@ -19,6 +19,7 @@ package clique
 import (
 	"bytes"
 	"encoding/json"
+	"sort"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/types"
@@ -56,6 +57,13 @@ type Snapshot struct {
 	Tally   map[common.Address]Tally    `json:"tally"`   // Current vote tally to avoid recalculating
 }
 
+// signers implements the sort interface to allow sorting a list of addresses
+type signers []common.Address
+
+func (s signers) Len() int           { return len(s) }
+func (s signers) Less(i, j int) bool { return bytes.Compare(s[i][:], s[j][:]) < 0 }
+func (s signers) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
+
 // newSnapshot creates a new snapshot with the specified startup parameters. This
 // method does not initialize the set of recent signers, so only ever use if for
 // the genesis block.
@@ -286,18 +294,12 @@ func (s *Snapshot) apply(headers []*types.Header) (*Snapshot, error) {
 
 // signers retrieves the list of authorized signers in ascending order.
 func (s *Snapshot) signers() []common.Address {
-	signers := make([]common.Address, 0, len(s.Signers))
-	for signer := range s.Signers {
-		signers = append(signers, signer)
+	sigs := make([]common.Address, 0, len(s.Signers))
+	for sig := range s.Signers {
+		sigs = append(sigs, sig)
 	}
-	for i := 0; i < len(signers); i++ {
-		for j := i + 1; j < len(signers); j++ {
-			if bytes.Compare(signers[i][:], signers[j][:]) > 0 {
-				signers[i], signers[j] = signers[j], signers[i]
-			}
-		}
-	}
-	return signers
+	sort.Sort(signers(sigs))
+	return sigs
 }
 
 // inturn returns if a signer at a given block height is in-turn or not.