X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fevaluate.cpp;h=ef33adf5d774a56fb306a6333c4774fd3fd11daa;hp=a1b04316e79b52f3ffb474596948ef1617123cf2;hb=8630d03dd4e1ec7e492ddf6c40d9d9e4cdba2a58;hpb=be7a03a957d5c2590a329f8f47acea8af2305adf

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index a1b04316..ef33adf5 100644
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -844,6 +844,8 @@ namespace {
     behind |= shift<Down>(behind);
     behind |= shift<Down+Down>(behind);
 
+    // Compute space score based on the number of safe squares and number of our pieces
+    // increased with number of total blocked pawns in position.
     int bonus = popcount(safe) + popcount(behind & safe & ~attackedBy[Them][ALL_PIECES]);
     int weight = pos.count<ALL_PIECES>(Us) - 3 + std::min(pe->blocked_count(), 9);
     Score score = make_score(bonus * weight * weight / 16, 0);
@@ -905,24 +907,36 @@ namespace {
     {
         if (pos.opposite_bishops())
         {
+            // For pure opposite colored bishops endgames use scale factor
+            // based on the number of passed pawns of the strong side.
             if (   pos.non_pawn_material(WHITE) == BishopValueMg
                 && pos.non_pawn_material(BLACK) == BishopValueMg)
                 sf = 18 + 4 * popcount(pe->passed_pawns(strongSide));
+            // For every other opposite colored bishops endgames use scale factor
+            // based on the number of all pieces of the strong side.
             else
                 sf = 22 + 3 * pos.count<ALL_PIECES>(strongSide);
         }
+        // For rook endgames with strong side not having overwhelming pawn number advantage
+        // and its pawns being on one flank and weak side protecting its pieces with a king
+        // use lower scale factor.
         else if (  pos.non_pawn_material(WHITE) == RookValueMg
                 && pos.non_pawn_material(BLACK) == RookValueMg
                 && pos.count<PAWN>(strongSide) - pos.count<PAWN>(~strongSide) <= 1
                 && bool(KingSide & pos.pieces(strongSide, PAWN)) != bool(QueenSide & pos.pieces(strongSide, PAWN))
                 && (attacks_bb<KING>(pos.square<KING>(~strongSide)) & pos.pieces(~strongSide, PAWN)))
             sf = 36;
+        // For queen vs no queen endgames use scale factor
+        // based on number of minors of side that doesn't have queen.
         else if (pos.count<QUEEN>() == 1)
             sf = 37 + 3 * (pos.count<QUEEN>(WHITE) == 1 ? pos.count<BISHOP>(BLACK) + pos.count<KNIGHT>(BLACK)
                                                         : pos.count<BISHOP>(WHITE) + pos.count<KNIGHT>(WHITE));
+        // In every other case use scale factor based on
+        // the number of pawns of the strong side reduced if pawns are on a single flank.
         else
             sf = std::min(sf, 36 + 7 * pos.count<PAWN>(strongSide)) - 4 * !pawnsOnBothFlanks;
 
+        // Reduce scale factor in case of pawns being on a single flank
         sf -= 4 * !pawnsOnBothFlanks;
     }
 
@@ -1046,6 +1060,8 @@ Value Eval::evaluate(const Position& pos) {
       bool  largePsq = psq * 16 > (NNUEThreshold1 + pos.non_pawn_material() / 64) * r50;
       bool  classical = largePsq || (psq > PawnValueMg / 4 && !(pos.this_thread()->nodes & 0xB));
 
+      // Use classical evaluation for really low piece endgames.
+      // The most critical case is a bishop + A/H file pawn vs naked king draw.
       bool strongClassical = pos.non_pawn_material() < 2 * RookValueMg && pos.count<PAWN>() < 2;
 
       v = classical || strongClassical ? Evaluation<NO_TRACE>(pos).value() : adjusted_NNUE();