Small cleanups

Corrects some incorrect or outdated comments.
Credit is shared with yaneurao (see 38e830a#commitcomment-131131500) and locutus2

closes #4852

No functional change.

diff --git a/src/movepick.h b/src/movepick.h
index f210f5387fcb222bb8a0728e4a9e413a2a7b583b..dc171c9ff5ba45143e66d5207f4fd9286e3b0a8b 100644 (file)
--- a/src/movepick.h
+++ b/src/movepick.h
@@ -32,7 +32,10 @@
 
 namespace Stockfish {
 
-constexpr int PAWN_HISTORY_SIZE = 512;
+constexpr int PAWN_HISTORY_SIZE = 512;  // has to be a power of 2
+
+static_assert((PAWN_HISTORY_SIZE & (PAWN_HISTORY_SIZE - 1)) == 0,
+              "PAWN_HISTORY_SIZE has to be a power of 2");
 
 inline int pawn_structure(const Position& pos) { return pos.pawn_key() & (PAWN_HISTORY_SIZE - 1); }
 

diff --git a/src/search.cpp b/src/search.cpp
index b7b51e0b3deb239a7b7c226aeed7781322bca651..ef98d862e6af7e9003bd4474af2a8c133641ade1 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -830,16 +830,19 @@ Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, boo
         }
     }
 
-    // Step 10. If the position doesn't have a ttMove, decrease depth by 2,
-    // or by 4 if the TT entry for the current position was hit and
+    // Step 10. Internal iterative reductions (~9 Elo)
+    // For PV nodes without a ttMove, we decrease depth by 2,
+    // or by 4 if the current position is present in the TT and
     // the stored depth is greater than or equal to the current depth.
-    // Use qsearch if depth is equal or below zero (~9 Elo)
+    // Use qsearch if depth <= 0.
     if (PvNode && !ttMove)
         depth -= 2 + 2 * (ss->ttHit && tte->depth() >= depth);
 
     if (depth <= 0)
         return qsearch<PV>(pos, ss, alpha, beta);
 
+    // For cutNodes without a ttMove, we decrease depth by 2
+    // if current depth >= 8.
     if (cutNode && depth >= 8 && !ttMove)
         depth -= 2;
 
@@ -1129,7 +1132,7 @@ moves_loop:  // When in check, search starts here
         if (PvNode)
             r--;
 
-        // Decrease reduction if ttMove has been singularly extended (~1 Elo)
+        // Decrease reduction if a quiet ttMove has been singularly extended (~1 Elo)
         if (singularQuietLMR)
             r--;
 
@@ -1194,7 +1197,7 @@ moves_loop:  // When in check, search starts here
         // Step 18. Full-depth search when LMR is skipped
         else if (!PvNode || moveCount > 1)
         {
-            // Increase reduction for cut nodes and not ttMove (~1 Elo)
+            // Increase reduction for cut nodes without ttMove (~1 Elo)
             if (!ttMove && cutNode)
                 r += 2;
 
@@ -1724,7 +1727,7 @@ void update_all_stats(const Position& pos,
 
 
 // Updates histories of the move pairs formed
-// by moves at ply -1, -2, -4, and -6 with current move.
+// by moves at ply -1, -2, -3, -4, and -6 with current move.
 void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus) {
 
     for (int i : {1, 2, 3, 4, 6})