From 231db5270acb2e673a641a1800be910ce345668a Mon Sep 17 00:00:00 2001
From: maksymivv <maksymivv@gmail.com>
Date: Fri, 18 Nov 2016 11:18:23 +0200
Subject: [PATCH] Difficulty algo

Difficulty algo cleanup, based on suggestions by Eugene
---
 ReleaseNotes.txt                |  8 +++++++
 src/CryptoNoteCore/Currency.cpp | 37 +++++++++++++++------------------
 2 files changed, 25 insertions(+), 20 deletions(-)

diff --git a/ReleaseNotes.txt b/ReleaseNotes.txt
index 324f87fb8b..26ec84094f 100644
--- a/ReleaseNotes.txt
+++ b/ReleaseNotes.txt
@@ -1,3 +1,11 @@
+Release notes Karbowanec 1.3.0
+
+- Bytecoin core 1.0.11 transition
+- New difficulty algorithm
+- Tail emission
+- Daemon restricted RPC mode
+- Fees for open remote node
+
 Release notes 1.0.11
 
 - New Bytecoin Wallet file format
diff --git a/src/CryptoNoteCore/Currency.cpp b/src/CryptoNoteCore/Currency.cpp
index 8b4e265370..f02a9caf7a 100755
--- a/src/CryptoNoteCore/Currency.cpp
+++ b/src/CryptoNoteCore/Currency.cpp
@@ -407,10 +407,13 @@ namespace CryptoNote {
 	difficulty_type Currency::nextDifficulty(uint8_t blockMajorVersion, std::vector<uint64_t> timestamps,
 		std::vector<difficulty_type> cumulativeDifficulties) const {
 
-		if (blockMajorVersion >= BLOCK_MAJOR_VERSION_2) {
+		// new difficulty calculation
+		// based on Zawy difficulty algorithm v1.0
+		// next Diff = Avg past N Diff * TargetInterval / Avg past N solve times
+		// as described at https://github.com/monero-project/research-lab/issues/3
+		// Window time span and total difficulty is taken instead of average as suggested by Eugene
 
-			// default CN with smaller window DIFFICULTY_WINDOW_V2
-			// without DIFFICULTY_CUT it gives very similar results to the Zawy's formula below
+		if (blockMajorVersion >= BLOCK_MAJOR_VERSION_2) {
 
 			size_t m_difficultyWindow_2 = CryptoNote::parameters::DIFFICULTY_WINDOW_V2;
 			assert(m_difficultyWindow_2 >= 2);
@@ -429,37 +432,31 @@ namespace CryptoNote {
 
 			sort(timestamps.begin(), timestamps.end());
 
-		/*	uint64_t timeSpan = timestamps[length - 1] - timestamps[0];
+			uint64_t timeSpan = timestamps.back() - timestamps.front();
 			if (timeSpan == 0) {
 				timeSpan = 1;
 			}
 
-			difficulty_type totalWork = cumulativeDifficulties[length - 1] - cumulativeDifficulties[0];
+			difficulty_type totalWork = cumulativeDifficulties.back() - cumulativeDifficulties.front();
 			assert(totalWork > 0);
 
-			uint64_t low, high;
+			// uint64_t nextDiffZ = totalWork * m_difficultyTarget / timeSpan; 
+
+ 			uint64_t low, high;
 			low = mul128(totalWork, m_difficultyTarget, &high);
+			// blockchain error "Difficulty overhead" if this function returns zero
 			if (high != 0 || low + timeSpan - 1 < low) {
 				return 0;
-			} 
-
-			uint64_t nextDiffAlt = (low + timeSpan - 1) / timeSpan; */
-		//	return nextDiffAlt;
-
-			// Zawy difficulty algorithm v1.0
-			// next Diff = Avg past N Diff * TargetInterval / Avg past N solve times
-			// this gives almost same results as modified CN version without cut above
+			}
 
-			uint64_t avgWindowDiff = (cumulativeDifficulties.back() - cumulativeDifficulties.front()) / cumulativeDifficulties.size();
-			uint64_t avgSolveTime = (timestamps.back() - timestamps.front()) / timestamps.size();
-			uint64_t nextDiffZ = avgWindowDiff * m_difficultyTarget / avgSolveTime;
+			uint64_t nextDiffZ = low / timeSpan;
 
+			// minimum limit
 			if (nextDiffZ <= 100000) {
-			nextDiffZ = 100000;
+				nextDiffZ = 100000;
 			}
-			
+
 			return nextDiffZ;
-		
 
 			// end of new difficulty calculation