feat: cache block hashes (bluealloy#71)

* feat: cache block hashes

Caches block hashes, but also computes a block hash based
on the block number if no block hash was returned from the
underlying database.

Retrieving block hashes can be expensive, but it is also
important that block hashes for different blocks
differ from each other

* chore: clippy

* refactor: move custom block hash to `EmptyDB`

crates/revm/src/db/in_memory_db.rs

@@ -28,6 +28,7 @@ pub struct CacheDB<ExtDB: DatabaseRef> {
     storage: Map<H160, Map<U256, U256>>,
     contracts: Map<H256, Bytes>,
     logs: Vec<Log>,
+    block_hashes: Map<U256, H256>,
     db: ExtDB,
 }
 
@@ -41,6 +42,7 @@ impl<ExtDB: DatabaseRef> CacheDB<ExtDB> {
             storage: Map::new(),
             contracts,
             logs: Vec::default(),
+            block_hashes: Map::new(),
             db,
         }
     }
@@ -103,7 +105,14 @@ impl<ExtDB: DatabaseRef> DatabaseCommit for CacheDB<ExtDB> {
 
 impl<ExtDB: DatabaseRef> Database for CacheDB<ExtDB> {
     fn block_hash(&mut self, number: U256) -> H256 {
-        self.db.block_hash(number)
+        match self.block_hashes.entry(number) {
+            Entry::Occupied(entry) => *entry.get(),
+            Entry::Vacant(entry) => {
+                let hash = self.db.block_hash(number);
+                entry.insert(hash);
+                hash
+            }
+        }
     }
 
     fn basic(&mut self, address: H160) -> AccountInfo {
@@ -155,7 +164,10 @@ impl<ExtDB: DatabaseRef> Database for CacheDB<ExtDB> {
 
 impl<ExtDB: DatabaseRef> DatabaseRef for CacheDB<ExtDB> {
     fn block_hash(&self, number: U256) -> H256 {
-        self.db.block_hash(number)
+        match self.block_hashes.get(&number) {
+            Some(entry) => *entry,
+            None => self.db.block_hash(number),
+        }
     }
 
     fn basic(&self, address: H160) -> AccountInfo {
@@ -202,8 +214,10 @@ impl DatabaseRef for EmptyDB {
     }
 
     // History related
-    fn block_hash(&self, _number: U256) -> H256 {
-        H256::default()
+    fn block_hash(&self, number: U256) -> H256 {
+        let mut buffer: [u8; 4 * 8] = [0; 4 * 8];
+        number.to_big_endian(&mut buffer);
+        H256::from_slice(&Keccak256::digest(&buffer))
     }
 }
 

crates/revm/src/specification.rs

@@ -124,9 +124,8 @@ mod spec_impl {
     spec!(FRONTIER);
 }
 
-pub use spec_impl::BERLIN::SpecImpl as BerlinSpec;
-pub use spec_impl::BYZANTINE::SpecImpl as ByzantineSpec;
-pub use spec_impl::FRONTIER::SpecImpl as FrontierSpec;
-pub use spec_impl::ISTANBUL::SpecImpl as IstanbulSpec;
-pub use spec_impl::LATEST::SpecImpl as LatestSpec;
-pub use spec_impl::LONDON::SpecImpl as LondonSpec;
+pub use spec_impl::{
+    BERLIN::SpecImpl as BerlinSpec, BYZANTINE::SpecImpl as ByzantineSpec,
+    FRONTIER::SpecImpl as FrontierSpec, ISTANBUL::SpecImpl as IstanbulSpec,
+    LATEST::SpecImpl as LatestSpec, LONDON::SpecImpl as LondonSpec,
+};