Merge pull request #237

41a95e7 add comment about avoiding overflow (smooth)
754a785 minimum subsidy for mining incentives, remove unused LEGACY_FEE define (smooth)

3 files changed, 13 insertions, 4 deletions

diff --git a/src/cryptonote_config.h b/src/cryptonote_config.h
index e26945086..e5df844e7 100644
--- a/src/cryptonote_config.h
+++ b/src/cryptonote_config.h
@@ -51,6 +51,7 @@
 // MONEY_SUPPLY - total number coins to be generated
 #define MONEY_SUPPLY                                    ((uint64_t)(-1))
 #define EMISSION_SPEED_FACTOR                           (20)
+#define FINAL_SUBSIDY_PER_MINUTE                        ((uint64_t)300000000000) // 3 * pow(10, 11)
 
 #define CRYPTONOTE_REWARD_BLOCKS_WINDOW                 100
 #define CRYPTONOTE_BLOCK_GRANTED_FULL_REWARD_ZONE       20000 //size of block (bytes) after which reward for block calculated using block size
@@ -61,9 +62,6 @@
 
 #define FEE_PER_KB                                      ((uint64_t)10000000000) // pow(10, 10)
 
-// temporarily to allow backward compatibility during the switch to per-kb
-//#define MINING_ALLOWED_LEGACY_FEE                       ((uint64_t)100000000000) // pow(10, 11)
-
 #define ORPHANED_BLOCKS_MAX_COUNT                       100
 
 
diff --git a/src/cryptonote_core/blockchain_storage.cpp b/src/cryptonote_core/blockchain_storage.cpp
index e2b6f2326..42269e05c 100644
--- a/src/cryptonote_core/blockchain_storage.cpp
+++ b/src/cryptonote_core/blockchain_storage.cpp
@@ -1709,7 +1709,14 @@ bool blockchain_storage::handle_block_to_main_chain(const block& bl, const crypt
   bei.bl = bl;
   bei.block_cumulative_size = cumulative_block_size;
   bei.cumulative_difficulty = current_diffic;
-  bei.already_generated_coins = already_generated_coins + base_reward;
+
+  // In the "tail" state when the minimum subsidy (implemented in get_block_reward) is in effect, the number of 
+  // coins will eventually exceed MONEY_SUPPLY and overflow a uint64. To prevent overflow, cap already_generated_coins 
+  // at MONEY_SUPPLY. already_generated_coins is only used to compute the block subsidy and MONEY_SUPPLY yields a 
+  // subsidy of 0 under the base formula and therefore the minimum subsidy >0 in the tail state.
+
+  bei.already_generated_coins = base_reward < (MONEY_SUPPLY-already_generated_coins) ? already_generated_coins + base_reward : MONEY_SUPPLY;
+
   if(m_blocks.size())
     bei.cumulative_difficulty += m_blocks.back().cumulative_difficulty;
 
diff --git a/src/cryptonote_core/cryptonote_basic_impl.cpp b/src/cryptonote_core/cryptonote_basic_impl.cpp
index a7416a7e4..f2d862e57 100644
--- a/src/cryptonote_core/cryptonote_basic_impl.cpp
+++ b/src/cryptonote_core/cryptonote_basic_impl.cpp
@@ -60,6 +60,10 @@ namespace cryptonote {
   //-----------------------------------------------------------------------------------------------
   bool get_block_reward(size_t median_size, size_t current_block_size, uint64_t already_generated_coins, uint64_t &reward) {
     uint64_t base_reward = (MONEY_SUPPLY - already_generated_coins) >> EMISSION_SPEED_FACTOR;
+    if (base_reward < FINAL_SUBSIDY_PER_MINUTE)
+    {
+      base_reward = FINAL_SUBSIDY_PER_MINUTE;
+    }
 
     //make it soft
     if (median_size < CRYPTONOTE_BLOCK_GRANTED_FULL_REWARD_ZONE) {