Remove DistanceRing #2107

Remove the DistanceRing array. This reduces the memory footprint by about 4kb. http://tests.stockfishchess.org/tests/view/5cba35350ebc5925cf020d7f LLR: 2.95 (-2.94,2.94) [-3.00,1.00] Total: 101421 W: 22491 L: 22528 D: 56402 No functional change.
official-stockfish · Apr 20, 2019 · a858b5a · a858b5a
1 parent bdeb01d
commit a858b5a
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Showing 3 changed files with 8 additions and 9 deletions.
diff --git a/src/bitboard.cpp b/src/bitboard.cpp
@@ -28,7 +28,6 @@ uint8_t PopCnt16[1 << 16];
 uint8_t SquareDistance[SQUARE_NB][SQUARE_NB];
 
 Bitboard LineBB[SQUARE_NB][SQUARE_NB];
-Bitboard DistanceRingBB[SQUARE_NB][8];
 Bitboard PseudoAttacks[PIECE_TYPE_NB][SQUARE_NB];
 Bitboard PawnAttacks[COLOR_NB][SQUARE_NB];
 Bitboard SquareBB[SQUARE_NB];
@@ -83,10 +82,7 @@ void Bitboards::init() {
 
   for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
       for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
-          {
               SquareDistance[s1][s2] = std::max(distance<File>(s1, s2), distance<Rank>(s1, s2));
-              DistanceRingBB[s1][SquareDistance[s1][s2]] |= s2;
-          }
 
   int steps[][5] = { {}, { 7, 9 }, { 6, 10, 15, 17 }, {}, {}, {}, { 1, 7, 8, 9 } };
 

diff --git a/src/bitboard.h b/src/bitboard.h
@@ -69,7 +69,6 @@ extern uint8_t PopCnt16[1 << 16];
 extern uint8_t SquareDistance[SQUARE_NB][SQUARE_NB];
 
 extern Bitboard LineBB[SQUARE_NB][SQUARE_NB];
-extern Bitboard DistanceRingBB[SQUARE_NB][8];
 extern Bitboard PseudoAttacks[PIECE_TYPE_NB][SQUARE_NB];
 extern Bitboard PawnAttacks[COLOR_NB][SQUARE_NB];
 extern Bitboard KingFlank[FILE_NB];

diff --git a/src/pawns.cpp b/src/pawns.cpp
@@ -212,11 +212,15 @@ Score Entry::do_king_safety(const Position& pos) {
   Square ksq = pos.square<KING>(Us);
   kingSquares[Us] = ksq;
   castlingRights[Us] = pos.castling_rights(Us);
-  int minKingPawnDistance = 0;
 
   Bitboard pawns = pos.pieces(Us, PAWN);
-  if (pawns)
-      while (!(DistanceRingBB[ksq][++minKingPawnDistance] & pawns)) {}
+  int minPawnDist = pawns ? 8 : 0;
+
+  if (pawns & PseudoAttacks[KING][ksq])
+      minPawnDist = 1;
+
+  else while (pawns)
+      minPawnDist = std::min(minPawnDist, distance(ksq, pop_lsb(&pawns)));
 
   Value bonus = evaluate_shelter<Us>(pos, ksq);
 
@@ -227,7 +231,7 @@ Score Entry::do_king_safety(const Position& pos) {
   if (pos.can_castle(Us | QUEEN_SIDE))
       bonus = std::max(bonus, evaluate_shelter<Us>(pos, relative_square(Us, SQ_C1)));
 
-  return make_score(bonus, -16 * minKingPawnDistance);
+  return make_score(bonus, -16 * minPawnDist);
 }
 
 // Explicit template instantiation