add macro fenced exponential memory decay

- src/NameGame.cc: add static weight function that memoizes exp for
  different weight lengths.

Signed-off-by: Aiden Woodruff <woodra@rpi.edu>

1 files changed, 25 insertions, 3 deletions

diff --git a/src/NameGame.cc b/src/NameGame.cc
index e427542..1454862 100644
--- a/src/NameGame.cc
+++ b/src/NameGame.cc
@@ -1,3 +1,4 @@
+#include <cmath>
 #include <fstream>
 #include <iomanip>
 #include <iostream>
@@ -119,12 +120,33 @@ void NameGame::runRound(int r) {
         strategy_record.push_back({r, speaker.GetId(), speaker().Val1, strategy});
 }
 
+#undef USE_EXP_WEIGHT
+#ifdef USE_EXP_WEIGHT
+float weight(int i) {
+        static std::vector<float> weight_table;
+        if (i < 0) throw std::invalid_argument("bad weight input");
+        while (i < weight_table.size()) {
+                float x = weight_table.size();
+                weight_table.push_back(std::exp(-x));
+        }
+        return weight_table[i];
+}
+#endif
+
 int NameGame::best_move(int nId) const {
         const auto& mem = graph.GetNDat(nId).Val2;
+#ifdef USE_EXP_WEIGHT
+        std::map<int, float> votes;
+        for (int i = 0; i < mem.Len(); ++i) {
+                int strategy = mem[i];
+                if (votes.count(strategy)) votes[strategy] += weight(i);
+                else votes[strategy] = weight(i);
+#else
         std::map<int, int> votes;
-        for (const auto& v : mem) {
-                if (votes.count(v)) votes[v] += 1;
-                else votes[v] = 1;
+        for (const auto& strategy : mem) {
+                if (votes.count(strategy)) votes[strategy] += 1;
+                else votes[strategy] = 1;
+#endif
         }
         if (votes.empty()) return 0;
         int best = std::max_element(votes.begin(), votes.end(),