wallet: select part of the fake outs from recent outputs

25% of the outputs are selected from the last 5 days (if possible),
in order to avoid the common case of sending recently received
outputs again. 25% and 5 days are subject to review later, since
it's just a wallet level change.

2 files changed, 28 insertions, 11 deletions

diff --git a/src/blockchain_db/lmdb/db_lmdb.cpp b/src/blockchain_db/lmdb/db_lmdb.cpp
index acb7d2cf6..b5459b56b 100644
--- a/src/blockchain_db/lmdb/db_lmdb.cpp
+++ b/src/blockchain_db/lmdb/db_lmdb.cpp
@@ -2657,7 +2657,7 @@ void BlockchainLMDB::get_output_tx_and_index(const uint64_t& amount, const std::
   LOG_PRINT_L3("db3: " << db3);
 }
 
-std::map<uint64_t, uint64_t> BlockchainLMDB::get_output_histogram(const std::vector<uint64_t> &amounts, bool unlocked) const
+std::map<uint64_t, std::tuple<uint64_t, uint64_t, uint64_t>> BlockchainLMDB::get_output_histogram(const std::vector<uint64_t> &amounts, bool unlocked, uint64_t recent_cutoff) const
 {
   LOG_PRINT_L3("BlockchainLMDB::" << __func__);
   check_open();
@@ -2665,7 +2665,7 @@ std::map<uint64_t, uint64_t> BlockchainLMDB::get_output_histogram(const std::vec
   TXN_PREFIX_RDONLY();
   RCURSOR(output_amounts);
 
-  std::map<uint64_t, uint64_t> histogram;
+  std::map<uint64_t, std::tuple<uint64_t, uint64_t, uint64_t>> histogram;
   MDB_val k;
   MDB_val v;
 
@@ -2683,7 +2683,7 @@ std::map<uint64_t, uint64_t> BlockchainLMDB::get_output_histogram(const std::vec
       mdb_size_t num_elems = 0;
       mdb_cursor_count(m_cur_output_amounts, &num_elems);
       uint64_t amount = *(const uint64_t*)k.mv_data;
-      histogram[amount] = num_elems;
+      histogram[amount] = std::make_tuple(num_elems, 0, 0);
     }
   }
   else
@@ -2694,13 +2694,13 @@ std::map<uint64_t, uint64_t> BlockchainLMDB::get_output_histogram(const std::vec
       int ret = mdb_cursor_get(m_cur_output_amounts, &k, &v, MDB_SET);
       if (ret == MDB_NOTFOUND)
       {
-        histogram[amount] = 0;
+        histogram[amount] = std::make_tuple(0, 0, 0);
       }
       else if (ret == MDB_SUCCESS)
       {
         mdb_size_t num_elems = 0;
         mdb_cursor_count(m_cur_output_amounts, &num_elems);
-        histogram[amount] = num_elems;
+        histogram[amount] = std::make_tuple(num_elems, 0, 0);
       }
       else
       {
@@ -2709,11 +2709,11 @@ std::map<uint64_t, uint64_t> BlockchainLMDB::get_output_histogram(const std::vec
     }
   }
 
-  if (unlocked) {
+  if (unlocked || recent_cutoff > 0) {
     const uint64_t blockchain_height = height();
-    for (auto i: histogram) {
-      uint64_t amount = i.first;
-      uint64_t num_elems = i.second;
+    for (std::map<uint64_t, std::tuple<uint64_t, uint64_t, uint64_t>>::iterator i = histogram.begin(); i != histogram.end(); ++i) {
+      uint64_t amount = i->first;
+      uint64_t num_elems = std::get<0>(i->second);
       while (num_elems > 0) {
         const tx_out_index toi = get_output_tx_and_index(amount, num_elems - 1);
         const uint64_t height = get_tx_block_height(toi.first);
@@ -2722,7 +2722,23 @@ std::map<uint64_t, uint64_t> BlockchainLMDB::get_output_histogram(const std::vec
         --num_elems;
       }
       // modifying second does not invalidate the iterator
-      i.second = num_elems;
+      std::get<1>(i->second) = num_elems;
+
+      if (recent_cutoff > 0)
+      {
+        uint64_t recent = 0;
+        while (num_elems > 0) {
+          const tx_out_index toi = get_output_tx_and_index(amount, num_elems - 1);
+          const uint64_t height = get_tx_block_height(toi.first);
+          const uint64_t ts = get_block_timestamp(height);
+          if (ts < recent_cutoff)
+            break;
+          --num_elems;
+          ++recent;
+        }
+        // modifying second does not invalidate the iterator
+        std::get<2>(i->second) = recent;
+      }
     }
   }
 
diff --git a/src/blockchain_db/lmdb/db_lmdb.h b/src/blockchain_db/lmdb/db_lmdb.h
index 9df4b86d1..6db5abca1 100644
--- a/src/blockchain_db/lmdb/db_lmdb.h
+++ b/src/blockchain_db/lmdb/db_lmdb.h
@@ -265,10 +265,11 @@ public:
    *
    * @param amounts optional set of amounts to lookup
    * @param unlocked whether to restrict count to unlocked outputs
+   * @param recent_cutoff timestamp to determine which outputs are recent
    *
    * @return a set of amount/instances
    */
-  std::map<uint64_t, uint64_t> get_output_histogram(const std::vector<uint64_t> &amounts, bool unlocked) const;
+  std::map<uint64_t, std::tuple<uint64_t, uint64_t, uint64_t>> get_output_histogram(const std::vector<uint64_t> &amounts, bool unlocked, uint64_t recent_cutoff) const;
 
 private:
   void do_resize(uint64_t size_increase=0);