Allow setting the draw value (default 0.5) in the rescorer.

src/selfplay/loop.cc

@@ -92,6 +92,11 @@ const OptionId kNnueBestMoveId{
 const OptionId kDeleteFilesId{"delete-files", "",
                               "Delete the input files after processing."};
 
+const OptionId kDrawValueId{"draw-value", "",
+                            "The value to use as a draw. Can bring the value "
+                            "of the draw closer to a loss or a win. "
+                            "Loss is 0, win is 1."};
+
 const OptionId kLogFileId{"logfile", "LogFile",
                           "Write log to that file. Special value <stderr> to "
                           "output the log to the console."};
@@ -453,6 +458,21 @@ std::string AsNnueString(const Position& p, Move m, float q, int result) {
   return out.str();
 }
 
+float QWithDrawValue(const V6TrainingData& data, bool useBest, float drawValue) {
+  const float original_q = useBest ? data.best_q : data.played_q;
+  const float original_d = useBest ? data.best_d : data.played_d;
+  // original_q is in [-1, 1]
+  const float w = (original_q + 1.0f - original_d) / 2.0f;
+  const float d = original_d;
+  const float l = w - original_q;
+  const float q =
+      w * 1.0f
+    + d * drawValue
+    + l * 0.0f;
+  // q in [0, 1], scale to [-1, 1]
+  return q * 2.0f - 1.0f;
+}
+
 struct ProcessFileFlags {
   bool delete_files : 1;
   bool nnue_best_score : 1;
@@ -461,7 +481,7 @@ struct ProcessFileFlags {
 
 void ProcessFile(const std::string& file, SyzygyTablebase* tablebase,
                  std::string outputDir, float distTemp, float distOffset,
-                 float dtzBoost, int newInputFormat,
+                 float dtzBoost, float drawValue, int newInputFormat,
                  std::string nnue_plain_file, ProcessFileFlags flags) {
   // Scope to ensure reader and writer are closed before deleting source file.
   {
@@ -1074,11 +1094,11 @@ void ProcessFile(const std::string& file, SyzygyTablebase* tablebase,
             Move m = MoveFromNNIndex(
                 flags.nnue_best_move ? chunk.best_idx : chunk.played_idx,
                 TransformForPosition(format, history));
-            float q = flags.nnue_best_score ? chunk.best_q : chunk.played_q;
+            const float q = QWithDrawValue(chunk, flags.nnue_best_score, drawValue);
             out << AsNnueString(p, m, q, round(chunk.result_q));
           } else if (i < moves.size()) {
-            out << AsNnueString(p, moves[i], chunk.best_q,
-                                round(chunk.result_q));
+            const float q = QWithDrawValue(chunk, true, drawValue);
+            out << AsNnueString(p, moves[i], q, round(chunk.result_q));
           }
           if (i < moves.size()) {
             history.Append(moves[i]);
@@ -1108,7 +1128,7 @@ void ProcessFile(const std::string& file, SyzygyTablebase* tablebase,
 void ProcessFiles(const std::vector<std::string>& files,
                   SyzygyTablebase* tablebase, std::string outputDir,
                   float distTemp, float distOffset, float dtzBoost,
-                  int newInputFormat, int offset, int mod,
+                  float drawValue, int newInputFormat, int offset, int mod,
                   std::string nnue_plain_file, ProcessFileFlags flags) {
   std::cerr << "Thread: " << offset << " starting" << std::endl;
   for (int i = offset; i < files.size(); i += mod) {
@@ -1117,7 +1137,7 @@ void ProcessFiles(const std::vector<std::string>& files,
       continue;
     }
     ProcessFile(files[i], tablebase, outputDir, distTemp, distOffset, dtzBoost,
-                newInputFormat, nnue_plain_file, flags);
+                drawValue, newInputFormat, nnue_plain_file, flags);
   }
 }
 
@@ -1214,6 +1234,7 @@ void RescoreLoop::RunLoop() {
   options_.Add<BoolOption>(kNnueBestScoreId) = true;
   options_.Add<BoolOption>(kNnueBestMoveId) = false;
   options_.Add<BoolOption>(kDeleteFilesId) = true;
+  options_.Add<FloatOption>(kDrawValueId, 0.0f, 1.0f) = 0.5f;
 
   SelfPlayTournament::PopulateOptions(&options_);
 
@@ -1299,7 +1320,9 @@ void RescoreLoop::RunLoop() {
             options_.GetOptionsDict().Get<std::string>(kOutputDirId),
             options_.GetOptionsDict().Get<float>(kTempId),
             options_.GetOptionsDict().Get<float>(kDistributionOffsetId),
-            dtz_boost, options_.GetOptionsDict().Get<int>(kNewInputFormatId),
+            dtz_boost,
+            options_.GetOptionsDict().Get<float>(kDrawValueId),
+            options_.GetOptionsDict().Get<int>(kNewInputFormatId),
             offset_val, threads,
             options_.GetOptionsDict().Get<std::string>(kNnuePlainFileId),
             flags);
@@ -1315,6 +1338,7 @@ void RescoreLoop::RunLoop() {
                  options_.GetOptionsDict().Get<float>(kTempId),
                  options_.GetOptionsDict().Get<float>(kDistributionOffsetId),
                  dtz_boost,
+                 options_.GetOptionsDict().Get<float>(kDrawValueId),
                  options_.GetOptionsDict().Get<int>(kNewInputFormatId), 0, 1,
                  options_.GetOptionsDict().Get<std::string>(kNnuePlainFileId),
                  flags);