Merge pull request #286 from ethcore/difficulty

Chain current difficulty calculation

db/src/storage.rs

@@ -307,7 +307,7 @@ impl Storage {
 		self.read_meta_u32(KEY_BEST_BLOCK_NUMBER)
 	}
 
-	fn _best_hash(&self) -> Option<H256> {
+	fn best_hash(&self) -> Option<H256> {
 		self.get(COL_META, KEY_BEST_BLOCK_HASH).map(|val| H256::from(&**val))
 	}
 
@@ -409,6 +409,14 @@ impl Storage {
 			best_number -= 1;
 			result.push(next);
 		}
+
+	}
+
+	pub fn difficulty(&self) -> f64 {
+		self.best_hash()
+			.and_then(|h| self.block_header_by_hash(&h))
+			.map(|header| header.bits.to_f64())
+			.unwrap_or(1.0f64)
 	}
 }
 
@@ -722,6 +730,7 @@ mod tests {
 	use chain::Block;
 	use super::super::{BlockRef, BlockLocation};
 	use test_data;
+	use primitives::Compact;
 
 	#[test]
 	fn open_store() {
@@ -1282,6 +1291,27 @@ mod tests {
 		assert_eq!(inserted_chain, BlockInsertedChain::Main, "h1 should become main chain");
 	}
 
+	#[test]
+	fn difficulty() {
+		let path = RandomTempPath::create_dir();
+		let store = Storage::new(path.as_path()).unwrap();
+
+		let genesis = test_data::genesis();
+		store.insert_block(&genesis)
+			.expect("Genesis should be inserted with no issues");
+
+		assert_eq!(1f64, store.difficulty(), "There should be minimum 1 difficulty for just the genesis block");
+
+		let block = test_data::block_builder()
+			.header().parent(genesis.hash()).bits(Compact::new(0x1b0404cb)).build()
+			.transaction().coinbase().build()
+			.build();
+		store.insert_block(&block)
+			.expect("Nest block with just nbits should be inserted with no issues");
+
+		assert_eq!(16307.420938523994f64, store.difficulty(), "There should be minimum updated difficulty for new best block");
+	}
+
 	#[test]
 	fn chain_for_side() {
 

primitives/src/compact.rs

@@ -76,6 +76,14 @@ impl Compact {
 		assert!(size < 256);
 		Compact(compact | (size << 24) as u32)
 	}
+
+	pub fn to_f64(&self) -> f64 {
+    	let max_body = f64::from(0x00ffff).ln();
+    	let scaland = f64::from(256).ln();
+    	let ln1 = f64::from(self.0 & 0x00ffffff).ln();
+    	let s1 = scaland * f64::from(0x1d - ((self.0 & 0xff000000) >> 24));
+		(max_body - ln1 + s1).exp()
+	}
 }
 
 #[cfg(test)]
@@ -113,6 +121,11 @@ mod tests {
 		let compact = Compact::new(0x05009234);
 		let compact2 = Compact::from_u256(compact.to_u256().unwrap());
 		assert_eq!(compact, compact2);
+	}
 
+	#[test]
+	fn difficulty() {
+		let nbits = Compact::new(0x1b0404cb);
+		assert_eq!(nbits.to_f64(), 16307.420938523994f64);
 	}
 }

primitives/src/lib.rs

@@ -13,3 +13,4 @@ pub use rustc_serialize::hex;
 pub use uint::U256;
 pub use hash::{H160, H256};
 pub use bytes::Bytes;
+pub use compact::Compact;