From a2f4090c059597afc42551e5543c3b55db701d1a Mon Sep 17 00:00:00 2001
From: Gav Wood <gav@ethcore.io>
Date: Thu, 28 Jan 2016 20:34:06 +0100
Subject: [PATCH] Fix difficulty calculation algo.

---
 res/ethereum/frontier.json       |  2 +-
 res/ethereum/homestead_test.json |  2 +-
 res/ethereum/morden.json         |  2 +-
 src/ethereum/ethash.rs           | 20 ++++++++++++++------
 src/spec.rs                      |  2 +-
 src/tests/chain.rs               | 14 ++++++++++++++
 6 files changed, 32 insertions(+), 10 deletions(-)

diff --git a/res/ethereum/frontier.json b/res/ethereum/frontier.json
index 9cb456ce8..43be680d2 100644
--- a/res/ethereum/frontier.json
+++ b/res/ethereum/frontier.json
@@ -3,7 +3,7 @@
 	"engineName": "Ethash",
 	"params": {
 		"accountStartNonce": "0x00",
-		"frontierCompatibilityModeLimit": "0xDBBA0",
+		"frontierCompatibilityModeLimit": "0xdbba0",
 		"maximumExtraDataSize": "0x20",
 		"tieBreakingGas": false,
 		"minGasLimit": "0x1388",
diff --git a/res/ethereum/homestead_test.json b/res/ethereum/homestead_test.json
index b11ef9740..1fb5dff80 100644
--- a/res/ethereum/homestead_test.json
+++ b/res/ethereum/homestead_test.json
@@ -3,7 +3,7 @@
 	"engineName": "Ethash",
 	"params": {
 		"accountStartNonce": "0x00",
-		"frontierCompatibilityModeLimit": "0",
+		"frontierCompatibilityModeLimit": 0,
 		"maximumExtraDataSize": "0x20",
 		"minGasLimit": "0x1388",
 		"tieBreakingGas": false,
diff --git a/res/ethereum/morden.json b/res/ethereum/morden.json
index 32fed0cab..cdcf8c7dc 100644
--- a/res/ethereum/morden.json
+++ b/res/ethereum/morden.json
@@ -3,7 +3,7 @@
 	"engineName": "Ethash",
 	"params": {
 		"accountStartNonce": "0x0100000",
-		"frontierCompatibilityModeLimit": "0xDBBA0",
+		"frontierCompatibilityModeLimit": "0xdbba0",
 		"maximumExtraDataSize": "0x20",
 		"tieBreakingGas": false,
 		"minGasLimit": "0x1388",
diff --git a/src/ethereum/ethash.rs b/src/ethereum/ethash.rs
index 019d764df..2ececec9b 100644
--- a/src/ethereum/ethash.rs
+++ b/src/ethereum/ethash.rs
@@ -59,9 +59,14 @@ impl Engine for Ethash {
 	}
 
 	fn schedule(&self, env_info: &EnvInfo) -> Schedule {
+		trace!(target: "client", "Creating schedule. param={:?}, fCML={}", self.spec().engine_params.get("frontierCompatibilityModeLimit"), self.u64_param("frontierCompatibilityModeLimit"));
 		match env_info.number < self.u64_param("frontierCompatibilityModeLimit") {
-			true => Schedule::new_frontier(),
-			_ => Schedule::new_homestead(),
+			true => {
+				Schedule::new_frontier()
+			},
+			_ => {
+				Schedule::new_homestead()
+			},
 		}
 	}
 
@@ -178,12 +183,15 @@ impl Ethash {
 			}
 		}
 		else {
-			let diff_inc = (header.timestamp - parent.timestamp) / 10;
-			if diff_inc <= 1 {
-				parent.difficulty + parent.difficulty / From::from(2048) * From::from(1 - diff_inc)
+			trace!(target: "ethash", "Calculating difficulty parent.difficulty={}, header.timestamp={}, parent.timestamp={}", parent.difficulty, header.timestamp, parent.timestamp);
+			//block_diff = parent_diff + parent_diff // 2048 * max(1 - (block_timestamp - parent_timestamp) // 10, -99)
+			if header.timestamp >= parent.timestamp + 10 {
+				let diff_inc = (header.timestamp - parent.timestamp) / 10;
+				parent.difficulty - parent.difficulty / From::from(2048) * From::from(min(diff_inc - 1, 99))
 			}
 			else {
-				parent.difficulty - parent.difficulty / From::from(2048) * From::from(max(diff_inc - 1, 99))
+				let minus_diff_inc = if parent.timestamp > header.timestamp {(parent.timestamp - header.timestamp) / 10} else {0};
+				parent.difficulty + parent.difficulty / From::from(2048) * From::from(minus_diff_inc + 1)
 			}
 		};
 		target = max(min_difficulty, target);
diff --git a/src/spec.rs b/src/spec.rs
index f4166eab2..77073eedd 100644
--- a/src/spec.rs
+++ b/src/spec.rs
@@ -16,7 +16,7 @@ pub fn gzip64res_to_json(source: &[u8]) -> Json {
 	Json::from_str(&s).expect("Json is invalid")
 }
 
-/// Convert JSON value to equivlaent RLP representation.
+/// Convert JSON value to equivalent RLP representation.
 // TODO: handle container types.
 fn json_to_rlp(json: &Json) -> Bytes {
 	match *json {
diff --git a/src/tests/chain.rs b/src/tests/chain.rs
index ca7884315..6518c546d 100644
--- a/src/tests/chain.rs
+++ b/src/tests/chain.rs
@@ -1,4 +1,6 @@
 use std::env;
+use log::{LogLevelFilter};
+use env_logger::LogBuilder;
 use super::test_common::*;
 use client::{BlockChainClient,Client};
 use pod_state::*;
@@ -10,7 +12,19 @@ pub enum ChainEra {
 	Homestead,
 }
 
+fn setup_log() {
+	let mut builder = LogBuilder::new();
+	builder.filter(None, LogLevelFilter::Info);
+
+	if env::var("RUST_LOG").is_ok() {
+		builder.parse(&env::var("RUST_LOG").unwrap());
+	}
+
+	builder.init().unwrap();
+}
+
 pub fn json_chain_test(json_data: &[u8], era: ChainEra) -> Vec<String> {
+	setup_log();
 	let json = Json::from_str(::std::str::from_utf8(json_data).unwrap()).expect("Json is invalid");
 	let mut failed = Vec::new();