Added difficulty retrival from Aura config (#11)

* Added difficulty retrival from Aura config

* Added default difficulty

consensus/aura/aura.go

@@ -56,13 +56,7 @@ var (
 	extraVanity = 32 // Fixed number of extra-data prefix bytes reserved for signer vanity
 	extraSeal   = 65 // Fixed number of extra-data suffix bytes reserved for signer seal
 
-	nonceAuthVote = hexutil.MustDecode("0xffffffffffffffff") // Magic nonce number to vote on adding a new signer
-	nonceDropVote = hexutil.MustDecode("0x0000000000000000") // Magic nonce number to vote on removing a signer.
-
 	uncleHash = types.CalcUncleHash(nil) // Always Keccak256(RLP([])) as uncles are meaningless outside of PoW.
-
-	diffInTurn = big.NewInt(2) // Block difficulty for in-turn signatures
-	diffNoTurn = big.NewInt(1) // Block difficulty for out-of-turn signatures
 )
 
 // Various error messages to mark blocks invalid. These should be private to
@@ -658,25 +652,9 @@ func (a *Aura) Seal(chain consensus.ChainReader, block *types.Block, results cha
 	return nil
 }
 
-// CalcDifficulty is the difficulty adjustment algorithm. It returns the difficulty
-// that a new block should have based on the previous blocks in the chain and the
-// current signer.
+// Returns difficulty constant from config
 func (a *Aura) CalcDifficulty(chain consensus.ChainReader, time uint64, parent *types.Header) *big.Int {
-	snap, err := a.snapshot(chain, parent.Number.Uint64(), parent.Hash(), nil)
-	if err != nil {
-		return nil
-	}
-	return CalcDifficulty(snap, a.signer)
-}
-
-// CalcDifficulty is the difficulty adjustment algorithm. It returns the difficulty
-// that a new block should have based on the previous blocks in the chain and the
-// current signer.
-func CalcDifficulty(snap *Snapshot, signer common.Address) *big.Int {
-	if snap.inturn(snap.Number+1, signer) {
-		return new(big.Int).Set(diffInTurn)
-	}
-	return new(big.Int).Set(diffNoTurn)
+	return new(big.Int).SetUint64(chain.Config().Aura.Difficulty)
 }
 
 // SealHash returns the hash of a block prior to it being sealed.

params/config.go

@@ -94,6 +94,7 @@ var (
 		Aura: &AuraConfig{
 			Period: 15,
 			Epoch:  30000,
+			Difficulty: 131072,
 		},
 	}
 
@@ -162,6 +163,7 @@ type CliqueConfig struct {
 type AuraConfig struct {
 	Period uint64 `json:"period"` // Number of seconds between blocks to enforce
 	Epoch  uint64 `json:"epoch"`  // Epoch length to reset votes and checkpoint
+	Difficulty uint64 `json:"difficulty"` // Constant block difficulty
 }
 
 // String implements the stringer interface, returning the consensus engine details.
@@ -378,3 +380,8 @@ func (c *ChainConfig) Rules(num *big.Int) Rules {
 	}
 	return Rules{ChainID: new(big.Int).Set(chainID), IsHomestead: c.IsHomestead(num), IsEIP150: c.IsEIP150(num), IsEIP155: c.IsEIP155(num), IsEIP158: c.IsEIP158(num), IsByzantium: c.IsByzantium(num)}
 }
+
+// Return diffulty rate for Aura concensus
+func (c *AuraConfig) GetDifficulty() (num *big.Int) {
+	return new(big.Int).SetUint64(c.Difficulty)
+}