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Simplify king file dependancy in evaluate_shelter()

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Remove the special value we used for the file of the king in the
evaluate_shelter() function, and compensate by tweaking some of
the ShelterStrength[] array values.

STC
LLR: 2.94 (-2.94,2.94) [-3.00,1.00]
Total: 17069 W: 3782 L: 3652 D: 9635
http://tests.stockfishchess.org/tests/view/5b75eb0d0ebc5902bdba8f3d

LTC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 42639 W: 6973 L: 6887 D: 28779
http://tests.stockfishchess.org/tests/view/5b75fd7f0ebc5902bdba906b

Closes https://github.com/official-stockfish/Stockfish/pull/1739

Bench: 4639508
This commit is contained in:
protonspring 2018-08-17 10:19:32 +02:00 • committed by Stéphane Nicolet
parent 881cab2525
commit d0f09de2d2
1 changed files with 6 additions and 8 deletions
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14
src/pawns.cpp
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@ -42,10 +42,10 @@ namespace {
// Strength of pawn shelter for our king by [distance from edge][rank].
// RANK_1 = 0 is used for files where we have no pawn, or pawn is behind our king.
constexpr Value ShelterStrength[int(FILE_NB) / 2][RANK_NB] = {
{ V( -3), V( 81), V( 93), V( 58), V( 39), V( 18), V( 25) },
{ V(-40), V( 61), V( 35), V(-49), V(-29), V(-11), V( -63) },
{ V( -7), V( 75), V( 23), V( -2), V( 32), V( 3), V( -45) },
{ V(-36), V(-13), V(-29), V(-52), V(-48), V(-67), V(-166) }
{ V( -6), V( 81), V( 93), V( 58), V( 39), V( 18), V( 25) },
{ V(-43), V( 61), V( 35), V(-49), V(-29), V(-11), V( -63) },
{ V(-10), V( 75), V( 23), V( -2), V( 32), V( 3), V( -45) },
{ V(-39), V(-13), V(-29), V(-52), V(-48), V(-67), V(-166) }
};
// Danger of enemy pawns moving toward our king by [distance from edge][rank].
@ -211,10 +211,8 @@ Value Entry::evaluate_shelter(const Position& pos, Square ksq) {
Bitboard ourPawns = b & pos.pieces(Us);
Bitboard theirPawns = b & pos.pieces(Them);
Value safety = (ourPawns & file_bb(ksq)) ? Value(5) : Value(-5);
if (shift<Down>(theirPawns) & (FileABB | FileHBB) & BlockRanks & ksq)
safety += Value(374);
Value safety = (shift<Down>(theirPawns) & (FileABB | FileHBB) & BlockRanks & ksq) ?
Value(374) : Value(5);
File center = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
for (File f = File(center - 1); f <= File(center + 1); ++f)