Make kingRing always 8 squares

Make kingRing always eight squares, extending the bitboard to the
F file if the king is on the H file, and to the C file if the king
is on the A file. This may deal with cases where Stockfish (like
many other engines) would shift the king around on the back rank
like g1h1, not because there is some imminent threat, but because
it makes king safety look a little better just because the king ring
had a smaller area.

STC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 34000 W: 7167 L: 6877 D: 19956
http://tests.stockfishchess.org/tests/view/5ab8216d0ebc5902932cbe64

LTC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 22574 W: 3576 L: 3370 D: 15628
http://tests.stockfishchess.org/tests/view/5ab84e6a0ebc5902932cbe72

How to continue from there?

This patch probably makes it easier to tune the king safety evaluation,
because the new regularity of the king ring size will make the king
safety function more continuous.

Closes https://github.com/official-stockfish/Stockfish/pull/1512

Bench: 5934103

diff --git a/src/bitboard.h b/src/bitboard.h
index 6032f47f6294b385847716154fe145009dfb5604..3d629de1abe986d63cbf3801f7d1a421cb8006ed 100644 (file)
--- a/src/bitboard.h
+++ b/src/bitboard.h
@@ -165,8 +165,9 @@ constexpr Bitboard make_bitboard(Square s, Squares... squares) {
 template<Direction D>
 constexpr Bitboard shift(Bitboard b) {
   return  D == NORTH      ?  b             << 8 : D == SOUTH      ?  b             >> 8
 template<Direction D>
 constexpr Bitboard shift(Bitboard b) {
   return  D == NORTH      ?  b             << 8 : D == SOUTH      ?  b             >> 8

-        : D == NORTH_EAST ? (b & ~FileHBB) << 9 : D == SOUTH_EAST ? (b & ~FileHBB) >> 7
-        : D == NORTH_WEST ? (b & ~FileABB) << 7 : D == SOUTH_WEST ? (b & ~FileABB) >> 9
+        : D == EAST       ? (b & ~FileHBB) << 1 : D == WEST       ? (b & ~FileABB) >> 1
+        : D == NORTH_EAST ? (b & ~FileHBB) << 9 : D == NORTH_WEST ? (b & ~FileABB) << 7 
+        : D == SOUTH_EAST ? (b & ~FileHBB) >> 7 : D == SOUTH_WEST ? (b & ~FileABB) >> 9

         : 0;
 }
 
         : 0;
 }
 

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 48c6e8ea1d7befaee0235485fcd07a4a28b5c412..c50d14c21aac50605e6a58d87fddbe83d49e285f 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -275,6 +275,12 @@ namespace {
         if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)
             kingRing[Us] |= shift<Up>(kingRing[Us]);
 
         if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)
             kingRing[Us] |= shift<Up>(kingRing[Us]);
 

+        if (file_of(pos.square<KING>(Us)) == FILE_H)
+            kingRing[Us] |= shift<WEST>(kingRing[Us]);
+
+        else if (file_of(pos.square<KING>(Us)) == FILE_A)
+            kingRing[Us] |= shift<EAST>(kingRing[Us]);
+

         kingAttackersCount[Them] = popcount(attackedBy[Us][KING] & pe->pawn_attacks(Them));
         kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
     }
         kingAttackersCount[Them] = popcount(attackedBy[Us][KING] & pe->pawn_attacks(Them));
         kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
     }