Add score_to_target method to ConsensusEngine

Author: Joon-Mo Yang

core/src/consensus/cuckoo/mod.rs

@@ -126,8 +126,7 @@ impl ConsensusEngine<CodeChainMachine> for Cuckoo {
         if !self.verifier.verify(&message, &seal.proof) {
             return Err(From::from(BlockError::InvalidProofOfWork))
         }
-        let max_hash = (U256::max_value() - *header.score()) / *header.score();
-        if U256::from(header.hash()) > max_hash {
+        if U256::from(header.hash()) > self.score_to_target(header.score()) {
             return Err(From::from(BlockError::InvalidScore(OutOfBounds {
                 min: Some(*header.score()),
                 max: Some(*header.score()),
@@ -167,4 +166,8 @@ impl ConsensusEngine<CodeChainMachine> for Cuckoo {
         let author = *block.header().author();
         self.machine.add_balance(block, &author, &self.params.block_reward)
     }
+
+    fn score_to_target(&self, score: &U256) -> U256 {
+        (U256::max_value() - *score) / *score
+    }
 }

core/src/consensus/mod.rs

@@ -37,7 +37,7 @@ use std::sync::{Arc, Weak};
 
 use ckey::ECDSASignature;
 use cnetwork::NetworkExtension;
-use ctypes::{Address, Bytes, H256};
+use ctypes::{Address, Bytes, H256, U256};
 use unexpected::{Mismatch, OutOfBounds};
 
 use self::epoch::{EpochVerifier, NoOp, PendingTransition};
@@ -212,6 +212,10 @@ pub trait ConsensusEngine<M: Machine>: Sync + Send {
     fn network_extension(&self) -> Option<Arc<NetworkExtension>> {
         None
     }
+
+    fn score_to_target(&self, _score: &U256) -> U256 {
+        U256::zero()
+    }
 }
 
 /// Results of a query of whether an epoch change occurred at the given block.