Implement 'old' multipv search.

It seems to be a waste of time to loop through all remaining root moves
after finishing each PV line. This patch skips this until we have reached
the last PV line (this is the way it was done in Glaurung and very early
versions of Stockfish).

No functional change in Single PV mode.

MultiPV=3 STC and LTC tests
LLR: 2.95 (-2.94,2.94) [0.00,5.00]
Total: 3113 W: 1248 L: 1064 D: 801

LLR: 2.95 (-2.94,2.94) [0.00,5.00]
Total: 2260 W: 848 L: 679 D: 733

Bench: 5023629

diff --git a/src/search.cpp b/src/search.cpp
index b9ce9a621175023d284ea8ba90c47ce3e29c881a..f47507f7e39b6ad6ba7a7ffaf3ebe2f17e1cd6e0 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -297,7 +297,7 @@ void Thread::search() {
       mainThread->bestMoveChanges = 0;
   }
 
-  size_t multiPV = Options["MultiPV"];
+  multiPV = Options["MultiPV"];
   Skill skill(Options["Skill Level"]);
 
   // When playing with strength handicap enable MultiPV search that we will
@@ -802,12 +802,20 @@ moves_loop: // When in check search starts from here
       if (move == excludedMove)
           continue;
 
-      // At root obey the "searchmoves" option and skip moves not listed in Root
-      // Move List. As a consequence any illegal move is also skipped. In MultiPV
-      // mode we also skip PV moves which have been already searched.
-      if (rootNode && !std::count(thisThread->rootMoves.begin() + thisThread->PVIdx,
-                                  thisThread->rootMoves.end(), move))
-          continue;
+      if (rootNode)
+      {
+          // At root obey the "searchmoves" option and skip moves not listed in Root
+          // Move List. As a consequence any illegal move is also skipped.
+          if (!std::count(thisThread->rootMoves.begin() + thisThread->PVIdx,
+                          thisThread->rootMoves.end(), move))
+              continue;
+
+          // In MultiPV mode we not only skip PV moves which have already been searched,
+          // but also any other move except we have reached the last PV line.
+          if (   thisThread->PVIdx + 1 < thisThread->multiPV
+              && move != ttMove)
+              continue;
+      }
 
       ss->moveCount = ++moveCount;
 
@@ -1527,7 +1535,7 @@ string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) {
   int elapsed = Time.elapsed() + 1;
   const RootMoves& rootMoves = pos.this_thread()->rootMoves;
   size_t PVIdx = pos.this_thread()->PVIdx;
-  size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());
+  size_t multiPV = pos.this_thread()->multiPV;
   uint64_t nodesSearched = Threads.nodes_searched();
   uint64_t tbHits = Threads.tb_hits() + (TB::RootInTB ? rootMoves.size() : 0);
 

diff --git a/src/thread.h b/src/thread.h
index 1397449733d8f7eebbc303ce879ff1dc7954b7ff..494fdb1583ec1a31ea909e1a3f56a56c5c06366e 100644 (file)
--- a/src/thread.h
+++ b/src/thread.h
@@ -60,7 +60,7 @@ public:
   Pawns::Table pawnsTable;
   Material::Table materialTable;
   Endgames endgames;
-  size_t PVIdx;
+  size_t PVIdx, multiPV;
   int selDepth, nmp_ply, nmp_odd;
   std::atomic<uint64_t> nodes, tbHits;