Make Blockchain::get_fee_quantization_mask() compile time

This also removes potential thread safety bug in that function.

src/common/powerof.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include <stdint.h>
+
+namespace tools
+{
+  template<uint64_t a, uint64_t b>
+  struct PowerOf
+  {
+    enum Data : uint64_t
+    {
+      // a^b = a * a^(b-1)
+      Value = a * PowerOf<a, b - 1>::Value,
+    };
+  };
+
+  template<uint64_t a>
+  struct PowerOf<a, 0>
+  {
+    enum Data : uint64_t
+    {
+      // a^0 = 1
+      Value = 1,
+    };
+  };
+}

src/cryptonote_core/blockchain.cpp

@@ -3710,19 +3710,6 @@ void Blockchain::check_ring_signature(const crypto::hash &tx_prefix_hash, const
   result = crypto::check_ring_signature(tx_prefix_hash, key_image, p_output_keys, sig.data()) ? 1 : 0;
 }
 
-//------------------------------------------------------------------
-uint64_t Blockchain::get_fee_quantization_mask()
-{
-  static uint64_t mask = 0;
-  if (mask == 0)
-  {
-    mask = 1;
-    for (size_t n = PER_KB_FEE_QUANTIZATION_DECIMALS; n < CRYPTONOTE_DISPLAY_DECIMAL_POINT; ++n)
-      mask *= 10;
-  }
-  return mask;
-}
-
 //------------------------------------------------------------------
 uint64_t Blockchain::get_dynamic_base_fee(uint64_t block_reward, size_t median_block_weight, uint8_t version)
 {

src/cryptonote_core/blockchain.h

@@ -51,6 +51,7 @@
 #include "string_tools.h"
 #include "rolling_median.h"
 #include "cryptonote_basic/cryptonote_basic.h"
+#include "common/powerof.h"
 #include "common/util.h"
 #include "cryptonote_protocol/cryptonote_protocol_defs.h"
 #include "rpc/core_rpc_server_commands_defs.h"
@@ -591,7 +592,10 @@ namespace cryptonote
      *
      * @return the fee quantized mask
      */
-    static uint64_t get_fee_quantization_mask();
+    static uint64_t get_fee_quantization_mask()
+    {
+      return tools::PowerOf<10, CRYPTONOTE_DISPLAY_DECIMAL_POINT - PER_KB_FEE_QUANTIZATION_DECIMALS>::Value;
+    }
 
     /**
      * @brief get dynamic per kB or byte fee for a given block weight