consensus/parlia: improve the check whether switched

consensus/parlia/snapshot.go

@@ -22,7 +22,6 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"math"
 	"sort"
 
 	lru "github.com/hashicorp/golang-lru"
@@ -272,11 +271,12 @@ func (s *Snapshot) apply(headers []*types.Header, chain consensus.ChainHeaderRea
 		snap.updateAttestation(header, chainConfig, s.config)
 		// change validator set
 		if number > 0 && number%s.config.Epoch == uint64(len(snap.Validators)/2) {
-			epochKey := math.MaxUint64 - header.Number.Uint64()/s.config.Epoch // impossible used as a block number
 			if chainConfig.IsBohr(header.Number, header.Time) {
 				// after switching the validator set, snap.Validators may become larger,
 				// then the unexpected second switch will happen, just skip it.
-				if _, ok := snap.Recents[epochKey]; ok {
+				// lastEpochBlock will be removed from Recents during the first switch.
+				lastEpochBlock := header.Number.Uint64() / s.config.Epoch * s.config.Epoch
+				if _, ok := snap.Recents[lastEpochBlock]; !ok {
 					continue
 				}
 			}
@@ -304,7 +304,6 @@ func (s *Snapshot) apply(headers []*types.Header, chain consensus.ChainHeaderRea
 			if chainConfig.IsBohr(header.Number, header.Time) {
 				// BEP-404: Clear Miner History when Switching Validators Set
 				snap.Recents = make(map[uint64]common.Address)
-				snap.Recents[epochKey] = common.Address{}
 				log.Debug("Recents are cleared up", "blockNumber", number)
 			} else {
 				oldLimit := len(snap.Validators)/2 + 1