Better clarify why recent generate_pawn_checks() works

[stockfish] / src / movegen.cpp

diff --git a/src/movegen.cpp b/src/movegen.cpp
index c51bc37f82068352870ba098230c976d6b53b35a..7558c89d63d6847261f6d3a62b3c63263d2d7ff4 100644 (file)
--- a/src/movegen.cpp
+++ b/src/movegen.cpp
@@ -29,7 +29,7 @@
 
 // Simple macro to wrap a very common while loop, no facny, no flexibility,
 // hardcoded list name 'mlist' and from square 'from'.
-#define SERIALIZE_MOVES(b) while (b) (*mlist++).move = make_move(from, pop_1st_bit<false>(&b))
+#define SERIALIZE_MOVES(b) while (b) (*mlist++).move = make_move(from, pop_1st_bit(&b))
 
 ////
 //// Local definitions
@@ -132,7 +132,7 @@ namespace {
 
 
 /// generate_captures generates() all pseudo-legal captures and queen
-/// promotions.  The return value is the number of moves generated.
+/// promotions. The return value is the number of moves generated.
 
 int generate_captures(const Position& pos, MoveStack* mlist) {
 
@@ -334,7 +334,7 @@ int generate_evasions(const Position& pos, MoveStack* mlist, Bitboard pinned) {
           // The checking pawn cannot be a discovered (bishop) check candidate
           // otherwise we were in check also before last double push move.
           assert(!bit_is_set(pos.discovered_check_candidates(them), checksq));
-          assert(count_1s<false>(b1) == 1 || count_1s<false>(b1) == 2);
+          assert(count_1s(b1) == 1 || count_1s(b1) == 2);
 
           b1 &= ~pinned;
           while (b1)
@@ -393,7 +393,6 @@ bool move_is_legal(const Position& pos, const Move m, Bitboard pinned) {
   assert(pinned == pos.pinned_pieces(pos.side_to_move()));
 
   Color us = pos.side_to_move();
-  Color them = opposite_color(us);
   Square from = move_from(m);
   Piece pc = pos.piece_on(from);
 
@@ -402,6 +401,7 @@ bool move_is_legal(const Position& pos, const Move m, Bitboard pinned) {
   if (color_of_piece(pc) != us)
       return false;
 
+  Color them = opposite_color(us);
   Square to = move_to(m);
 
   // En passant moves
@@ -791,9 +791,11 @@ namespace {
     // Direct checks. These are possible only for pawns on neighboring files
     // and in the two ranks that, after the push, are in front of the enemy king.
     b1 = pawns & neighboring_files_bb(ksq) & ~dc;
-    b2 = rank_bb(ksq + 2 * TDELTA_S) | rank_bb(ksq + 3 * TDELTA_S);
-    b1 &= b2;
-    if (!b1)
+
+    // We can get false positives if (ksq + x) is not in [0,63] range but
+    // is not a problem, they will be filtered out later.
+    b2 = b1 & (rank_bb(ksq + 2 * TDELTA_S) | rank_bb(ksq + 3 * TDELTA_S));
+    if (!b2)
         return mlist;
 
     // Direct checks, single pawn pushes