core: dynamic fee algorithm from ArticMine

The fee will vary based on the base reward and the current
block size limit:

fee = (R/R0) * (M0/M) * F0

R: base reward
R0: reference base reward (10 monero)
M: block size limit
M0: minimum block size limit (60000)
F0: 0.002 monero

Starts applying at v4

1 files changed, 52 insertions, 0 deletions

diff --git a/src/cryptonote_core/blockchain.cpp b/src/cryptonote_core/blockchain.cpp
index 9ea023a4c..c92ee6c9b 100644
--- a/src/cryptonote_core/blockchain.cpp
+++ b/src/cryptonote_core/blockchain.cpp
@@ -46,6 +46,7 @@
 #include "misc_language.h"
 #include "profile_tools.h"
 #include "file_io_utils.h"
+#include "common/int-util.h"
 #include "common/boost_serialization_helper.h"
 #include "warnings.h"
 #include "crypto/hash.h"
@@ -2709,6 +2710,57 @@ void Blockchain::check_ring_signature(const crypto::hash &tx_prefix_hash, const
 }
 
 //------------------------------------------------------------------
+uint64_t Blockchain::get_dynamic_per_kb_fee(uint64_t block_reward, size_t median_block_size)
+{
+  if (median_block_size < CRYPTONOTE_BLOCK_GRANTED_FULL_REWARD_ZONE_V2)
+    median_block_size = CRYPTONOTE_BLOCK_GRANTED_FULL_REWARD_ZONE_V2;
+
+  uint64_t unscaled_fee_per_kb = (DYNAMIC_FEE_PER_KB_BASE_FEE * CRYPTONOTE_BLOCK_GRANTED_FULL_REWARD_ZONE_V2 / median_block_size);
+  uint64_t hi, lo = mul128(unscaled_fee_per_kb, block_reward, &hi);
+  static_assert(DYNAMIC_FEE_PER_KB_BASE_BLOCK_REWARD % 1000000 == 0, "DYNAMIC_FEE_PER_KB_BASE_BLOCK_REWARD must be divisible by 1000000");
+  static_assert(DYNAMIC_FEE_PER_KB_BASE_BLOCK_REWARD / 1000000 <= std::numeric_limits<uint32_t>::max(), "DYNAMIC_FEE_PER_KB_BASE_BLOCK_REWARD is too large");
+  // divide in two steps, since the divisor must be 32 bits, but DYNAMIC_FEE_PER_KB_BASE_BLOCK_REWARD isn't
+  div128_32(hi, lo, DYNAMIC_FEE_PER_KB_BASE_BLOCK_REWARD / 1000000, &hi, &lo);
+  div128_32(hi, lo, 1000000, &hi, &lo);
+  assert(hi == 0);
+
+  return lo;
+}
+
+//------------------------------------------------------------------
+bool Blockchain::check_fee(size_t blob_size, uint64_t fee) const
+{
+  const uint8_t version = get_current_hard_fork_version();
+
+  uint64_t fee_per_kb;
+  if (version < HF_VERSION_DYNAMIC_FEE)
+  {
+    fee_per_kb = FEE_PER_KB;
+  }
+  else
+  {
+    uint64_t median = m_current_block_cumul_sz_limit / 2;
+    uint64_t already_generated_coins = m_db->height() ? m_db->get_block_already_generated_coins(m_db->height() - 1) : 0;
+    uint64_t base_reward;
+    if (!get_block_reward(median, 1, already_generated_coins, base_reward, version))
+      return false;
+    fee_per_kb = get_dynamic_per_kb_fee(base_reward, median);
+  }
+  LOG_PRINT_L2("Using " << print_money(fee) << "/kB fee");
+
+  uint64_t needed_fee = blob_size / 1024;
+  needed_fee += (blob_size % 1024) ? 1 : 0;
+  needed_fee *= fee_per_kb;
+
+  if (fee < needed_fee)
+  {
+    LOG_PRINT_L1("transaction fee is not enough: " << print_money(fee) << ", minimum fee: " << print_money(needed_fee));
+    return false;
+  }
+  return true;
+}
+
+//------------------------------------------------------------------
 // This function checks to see if a tx is unlocked.  unlock_time is either
 // a block index or a unix time.
 bool Blockchain::is_tx_spendtime_unlocked(uint64_t unlock_time) const