add lwma-2

src/cryptonote_basic/difficulty.cpp

@@ -240,4 +240,37 @@ namespace cryptonote {
     next_difficulty = static_cast<uint64_t>(nextDifficulty);
     return next_difficulty;
   }
+
+// LWMA-2 difficulty algorithm
+// Copyright (c) 2017-2018 Zawy, MIT License
+// See commented version in https://github.com/zawy12/difficulty-algorithms/issues/3 
+// for required config file changes.
+
+difficulty_type next_difficulty_v3(std::vector<std::uint64_t> timestamps, std::vector<difficulty_type> cumulative_difficulties) {
+ 
+    int64_t  T = DIFFICULTY_TARGET_V2;
+    int64_t  N = DIFFICULTY_WINDOW_V2;
+    int64_t  FTL = CRYPTONOTE_BLOCK_FUTURE_TIME_LIMIT_V3;
+    int64_t  L(0), ST, sum_3_ST(0), next_D, prev_D;
+
+    // TODO: change initial_difficulty_guess before v9 mainnet hard fork 
+    // if ( height >= fork_height && height <= fork_height+N )  { return difficulty_guess; }
+    uint64_t initial_difficulty_guess = 100;
+    if (timestamps.size() <= static_cast<uint64_t>(N)) {
+      return initial_difficulty_guess;
+    }
+
+    for ( int64_t i = 1; i <= N; i++) {
+      ST = std::max(-FTL, std::min( (int64_t)(timestamps[i]) - (int64_t)(timestamps[i-1]), 6*T));
+      L +=  ST * i ;
+      if ( i > N-3 ) { sum_3_ST += ST; }
+    }
+
+    next_D = ((cumulative_difficulties[N] - cumulative_difficulties[0])*T*(N+1)*99)/(100*2*L);
+
+    prev_D = cumulative_difficulties[N] - cumulative_difficulties[N-1];
+    if ( sum_3_ST < (8*T)/10) {  next_D = (prev_D*110)/100; }
+
+    return static_cast<uint64_t>(next_D);
+  }
 }

src/cryptonote_basic/difficulty.h

@@ -54,4 +54,5 @@ namespace cryptonote
     bool check_hash(const crypto::hash &hash, difficulty_type difficulty);
     difficulty_type next_difficulty(std::vector<std::uint64_t> timestamps, std::vector<difficulty_type> cumulative_difficulties, size_t target_seconds);
     difficulty_type next_difficulty_v2(std::vector<std::uint64_t> timestamps, std::vector<difficulty_type> cumulative_difficulties, size_t target_seconds);
+    difficulty_type next_difficulty_v3(std::vector<std::uint64_t> timestamps, std::vector<difficulty_type> cumulative_difficulties);
 }

src/cryptonote_core/blockchain.cpp

@@ -833,8 +833,12 @@ difficulty_type Blockchain::get_difficulty_for_next_block()
   size_t target = DIFFICULTY_TARGET_V2;
   if (version == 7) {
     return next_difficulty(timestamps, difficulties, target);
-  } else {
+  } 
+  else if (version == 8) {
     return next_difficulty_v2(timestamps, difficulties, target);
+    }
+  else {
+    return next_difficulty_v3(timestamps, difficulties);
   }
 }
 //------------------------------------------------------------------
@@ -1047,8 +1051,12 @@ difficulty_type Blockchain::get_next_difficulty_for_alternative_chain(const std:
   // calculate the difficulty target for the block and return it
   if (version == 7) {
     return next_difficulty(timestamps, cumulative_difficulties, target);
-  } else {
+  } 
+  else if (version == 8) {
     return next_difficulty_v2(timestamps, cumulative_difficulties, target);
+  }  
+  else {
+    return next_difficulty_v3(timestamps, cumulative_difficulties);
   }
 }