Cumulative fixes to make working with consensus-pow easier

core/consensus/pow/primitives/Cargo.toml

@@ -10,6 +10,7 @@ substrate-client = { path = "../../../client", default-features = false }
 rstd = { package = "sr-std", path = "../../../sr-std", default-features = false }
 sr-primitives = { path = "../../../sr-primitives", default-features = false }
 primitives = { package = "substrate-primitives", path = "../../../primitives", default-features = false }
+codec = { package = "parity-scale-codec", version = "1.0.0", default-features = false, features = ["derive"] }
 
 [features]
 default = ["std"]
@@ -18,4 +19,5 @@ std = [
 	"substrate-client/std",
 	"sr-primitives/std",
 	"primitives/std",
+	"codec/std",
 ]

core/consensus/pow/primitives/src/lib.rs

@@ -20,17 +20,46 @@
 
 use rstd::vec::Vec;
 use sr_primitives::ConsensusEngineId;
+use codec::Decode;
+use substrate_client::decl_runtime_apis;
 
 /// The `ConsensusEngineId` of PoW.
 pub const POW_ENGINE_ID: ConsensusEngineId = [b'p', b'o', b'w', b'_'];
 
-/// Type of difficulty.
-///
-/// For runtime designed for Substrate, it's always possible to fit its total
-/// difficulty range under `u128::max_value()` because it can be freely scaled
-/// up or scaled down. Very few PoW chains use difficulty values
-/// larger than `u128::max_value()`.
-pub type Difficulty = u128;
-
 /// Type of seal.
 pub type Seal = Vec<u8>;
+
+/// Define methods that total difficulty should implement.
+pub trait TotalDifficulty {
+	fn increment(&mut self, other: Self);
+}
+
+impl TotalDifficulty for primitives::U256 {
+	fn increment(&mut self, other: Self) {
+		let ret = self.saturating_add(other);
+		*self = ret;
+	}
+}
+
+impl TotalDifficulty for u128 {
+	fn increment(&mut self, other: Self) {
+		let ret = self.saturating_add(other);
+		*self = ret;
+	}
+}
+
+decl_runtime_apis! {
+	/// API necessary for timestamp-based difficulty adjustment algorithms.
+	pub trait TimestampApi<Moment: Decode> {
+		/// Return the timestamp in the current block.
+		fn timestamp() -> Moment;
+	}
+
+	/// API for those chains that put their difficulty adjustment algorithm directly
+	/// onto runtime. Note that while putting difficulty adjustment algorithm to
+	/// runtime is safe, putting the PoW algorithm on runtime is not.
+	pub trait DifficultyApi<Difficulty: Decode> {
+		/// Return the target difficulty of the next block.
+		fn difficulty() -> Difficulty;
+	}
+}