Minimal thinking time, even if only one rootMove.

without search, the eval returned can be misleading (e.g. mate instead of draw),
leading to wrong adjudication. With a minimal search, this is avoided.
This patch leads to 1ms long searches if there is only 1 move,
similar patches all indicate a small Elo gain.

Fixes https://github.com/official-stockfish/Stockfish/issues/2707

Passed non-regression STC:
LLR: 2.93 (-2.94,2.94) {-1.50,0.50}
Total: 22312 W: 4350 L: 4204 D: 13758
Ptnml(0-2): 323, 2488, 5437, 2536, 372
https://tests.stockfishchess.org/tests/view/5ed562b0f29b40b0fc95a7d0

closes https://github.com/official-stockfish/Stockfish/pull/2709

Bench: 4733799

diff --git a/src/search.cpp b/src/search.cpp
index 1e133447d381b547f97d9ea93ab7aa7321d862f7..35110538170c5cb03732a955b1cbe4b616eb7dc2 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -556,9 +556,11 @@ void Thread::search() {
           }
           double bestMoveInstability = 1 + totBestMoveChanges / Threads.size();
 
           }
           double bestMoveInstability = 1 + totBestMoveChanges / Threads.size();
 

-          // Stop the search if we have only one legal move, or if available time elapsed
-          if (   rootMoves.size() == 1
-              || Time.elapsed() > Time.optimum() * fallingEval * reduction * bestMoveInstability)
+          double totalTime = rootMoves.size() == 1 ? 0 :
+                             Time.optimum() * fallingEval * reduction * bestMoveInstability;
+
+          // Stop the search if we have exceeded the totalTime, at least 1ms search.
+          if (Time.elapsed() > totalTime)

           {
               // If we are allowed to ponder do not stop the search now but
               // keep pondering until the GUI sends "ponderhit" or "stop".
           {
               // If we are allowed to ponder do not stop the search now but
               // keep pondering until the GUI sends "ponderhit" or "stop".


@@ -569,7 +571,7 @@ void Thread::search() {
           }
           else if (   Threads.increaseDepth
                    && !mainThread->ponder
           }
           else if (   Threads.increaseDepth
                    && !mainThread->ponder

-                   && Time.elapsed() > Time.optimum() * fallingEval * reduction * bestMoveInstability * 0.6)
+                   && Time.elapsed() > totalTime * 0.6)

                    Threads.increaseDepth = false;
           else
                    Threads.increaseDepth = true;
                    Threads.increaseDepth = false;
           else
                    Threads.increaseDepth = true;