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Introduce trained PSQT depending on king position
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This patch introduces PSQ tables dependent on the attacking/defending king position. Similarly to regular PSQ tables, these can be efficiently updated for most moves, and only need to be recomputed from scratch after a king move. The king's position is encoded in a mirrored fashion.

The current table has been trained from a dataset of roughly 8M games at depth 6 (generated using the branch data_gen).

The default table is embedded in the binary using incbin.

STC: LLR: 2.94/2.94<0.00, 6.00> Elo diff: 70.84 [52.71, 89.35] (95%)
Games: 728 W: 271 L: 124 D: 333 Draw ratio: 45.7%
Pntl: [10, 57, 117, 135, 44]

LTC: LLR: 2.95/2.94<0.00, 6.00> Elo diff: 87.82 [69.86, 106.26] (95%)
Games: 608 W: 227 L: 76 D: 305 Draw ratio: 50.2%
Pntl: [2, 35, 113, 117, 36]

Closes #12

Bench: 2169197
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@ruicoelhopedro
ruicoelhopedro authored Nov 6, 2022
1 parent 567797f commit 1aa3bb3
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Showing 12 changed files with 696 additions and 98 deletions.
Binary file added psqt-769d9df255ea.dat
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24 changes: 15 additions & 9 deletions src/Evaluation.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -74,15 +74,21 @@ MixedScore piece_square_value(Board board, EvalData& eval)
{
eval.fields[WHITE].placement = MixedScore(0, 0);
eval.fields[BLACK].placement = MixedScore(0, 0);
Bitboard bb;

for (auto piece : { PAWN, KNIGHT, BISHOP, ROOK, QUEEN, KING })
Square king_sq[] = { board.get_pieces<WHITE, KING>().bitscan_forward(),
board.get_pieces<BLACK, KING>().bitscan_forward() };

for (PieceType p : { PAWN, KNIGHT, BISHOP, ROOK, QUEEN })
{
for (auto turn : { WHITE, BLACK })
for (Turn t : { WHITE, BLACK })
{
bb = board.get_pieces(turn, piece);
while (bb)
eval.fields[turn].placement += piece_square(piece, bb.bitscan_forward_reset(), turn);
Bitboard b = board.get_pieces(t, p);
while (b)
{
Square s = b.bitscan_forward_reset();
eval.fields[t].placement += piece_square(p, s, t, king_sq[WHITE], WHITE)
+ piece_square(p, s, t, king_sq[BLACK], BLACK);
}
}
}

Expand Down Expand Up @@ -490,8 +496,8 @@ Score evaluation(const Board& board, EvalData& data, Thread& thread)
MaterialEntry* me = probe_material(board, thread.m_material_table);
mixed_result += me->imbalance();

// Material and PSQT: incrementally updated in the position
mixed_result += board.material() + board.psq();
// Material incrementally updated in the position
mixed_result += board.material();

// Pawn structure
mixed_result += pawns(board, data);
Expand All @@ -512,7 +518,7 @@ Score evaluation(const Board& board, EvalData& data, Thread& thread)
mixed_result += passed<WHITE>(board, data) - passed<BLACK>(board, data);

// Tapered eval
Score result = scale(board, data, mixed_result);
Score result = scale(board, data, mixed_result) + board.psq();

// We don't return exact draw scores -> add one unit to the moving side
if (result == SCORE_DRAW)
Expand Down
91 changes: 91 additions & 0 deletions src/PieceSquareTables.cpp
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Original file line number Diff line number Diff line change
@@ -0,0 +1,91 @@
#include "Types.hpp"
#include "PieceSquareTables.hpp"
#include <iostream>
#include <fstream>
#include <string>

namespace PSQT
{
const FeatureType* psqt_data;


INCBIN(FeatureType, EmbeddedPSQT, PSQT_Default_File);


void init()
{
psqt_data = nullptr;
load(PSQT_Default_File);
}


void load(std::string file)
{
if (psqt_data)
clean();

if (file == "" || file == PSQT_Default_File)
{
psqt_data = gEmbeddedPSQTData;
}
else
{
std::ifstream input(file, std::ios_base::binary);
if (!input.is_open())
{
std::cerr << "Failed to open PSQ input file!" << std::endl;
std::abort();
}

psqt_data = new FeatureType[NUM_FEATURES];

if(!input.read(const_cast<char*>(reinterpret_cast<const char*>(psqt_data)), NUM_FEATURES * sizeof(FeatureType)))
{
std::cerr << "Failed to read PSQ data!" << std::endl;
std::abort();
}
}
}


void clean()
{
if (psqt_data != gEmbeddedPSQTData)
delete[] psqt_data;
psqt_data = nullptr;
}
}


Score piece_square(PieceType piece, Square square, Turn turn, Square king_sq, Turn king_turn)
{
// No PSQ data for the king
if (piece == KING)
return 0;

// Vertical mirror for black
if (turn == BLACK)
{
king_turn = ~king_turn;
square = vertical_mirror(square);
king_sq = vertical_mirror(king_sq);
}

// Horiziontal mirror if king on the files E to H
if (file(king_sq) >= 4)
{
square = horizontal_mirror(square);
king_sq = horizontal_mirror(king_sq);
}

// Compute corrected king index (since we are mirrored there are only 4 files)
int king_index = 4 * rank(king_sq) + file(king_sq);

// Compute PSQ table index
int index = square
+ piece * NUM_SQUARES
+ king_index * (NUM_SQUARES * (NUM_PIECE_TYPES - 1))
+ king_turn * (NUM_SQUARES * (NUM_PIECE_TYPES - 1) * NUM_SQUARES / 2);

return PSQT::psqt_data[index];
}
99 changes: 22 additions & 77 deletions src/PieceSquareTables.hpp
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Original file line number Diff line number Diff line change
@@ -1,6 +1,9 @@
#pragma once
#include "incbin/incbin.h"
#include "Types.hpp"

#define PSQT_Default_File "psqt-769d9df255ea.dat"

using S = MixedScore;

constexpr S PawnValue( 125, 200);
Expand Down Expand Up @@ -37,88 +40,30 @@ constexpr Score piece_value_eg[] = { PawnValue.endgame(),
0, // Empty
0 }; // PIECE_NONE

// Tables stolen from Stockfish using the implicitly mirrored convention
constexpr S psq_table[][8][4] = {
{ // Knight
{ S(-175, -96), S(-92, -65), S(-74, -49), S(-73, -21) },
{ S( -77, -67), S(-41, -54), S(-27, -18), S(-15, 8) },
{ S( -61, -40), S(-17, -27), S( 6, -8), S( 12, 29) },
{ S( -35, -35), S( 8, -2), S( 40, 13), S( 49, 28) },
{ S( -34, -45), S( 13, -16), S( 44, 9), S( 51, 39) },
{ S( -9, -51), S( 22, -44), S( 58, -16), S( 53, 17) },
{ S( -67, -69), S(-27, -50), S( 4, -51), S( 37, 12) },
{ S(-201, -100), S(-83, -88), S(-56, -56), S(-26, -17) }
},
{ // Bishop
{ S(-37, -40), S( -4, -21), S( -6, -26), S(-16, -8) },
{ S(-11, -26), S( 6, -9), S( 13, -12), S( 3, 1) },
{ S( -5, -11), S( 15, -1), S( -4, -1), S( 12, 7) },
{ S( -4, -14), S( 8, -4), S( 18, 0), S( 27, 12) },
{ S( -8, -12), S( 20, -1), S( 15, -10), S( 22, 11) },
{ S(-11, -21), S( 4, 4), S( 1, 3), S( 8, 4) },
{ S(-12, -22), S(-10, -14), S( 4, -1), S( 0, 1) },
{ S(-34, -32), S( 1, -29), S(-10, -26), S(-16, -17) }
},
{ // Rook
{ S(-31, -9), S(-20, -13), S(-14, -10), S(-5, -9) },
{ S(-21, -12), S(-13, -9), S( -8, -1), S( 6, -2) },
{ S(-25, 6), S(-11, -8), S( -1, -2), S( 3, -6) },
{ S(-13, -6), S( -5, 1), S( -4, -9), S(-6, 7) },
{ S(-27, -5), S(-15, 8), S( -4, 7), S( 3, -6) },
{ S(-22, 6), S( -2, 1), S( 6, -7), S(12, 10) },
{ S( -2, 4), S( 12, 5), S( 16, 20), S(18, -5) },
{ S(-17, 18), S(-19, 0), S( -1, 19), S( 9, 13) }
},
{ // Queen
{ S( 3, -69), S(-5, -57), S(-5, -47), S( 4, -26) },
{ S(-3, -54), S( 5, -31), S( 8, -22), S(12, -4) },
{ S(-3, -39), S( 6, -18), S(13, -9), S( 7, 3) },
{ S( 4, -23), S( 5, -3), S( 9, 13), S( 8, 24) },
{ S( 0, -29), S(14, -6), S(12, 9), S( 5, 21) },
{ S(-4, -38), S(10, -18), S( 6, -11), S( 8, 1) },
{ S(-5, -50), S( 6, -27), S(10, -24), S( 8, -8) },
{ S(-2, -74), S(-2, -52), S( 1, -43), S(-2, -34) }
},
{ // King
{ S(271, 1), S(327, 45), S(271, 85), S(198, 76) },
{ S(278, 53), S(303, 100), S(234, 133), S(179, 135) },
{ S(195, 88), S(258, 130), S(169, 169), S(120, 175) },
{ S(164, 103), S(190, 156), S(138, 172), S( 98, 172) },
{ S(154, 96), S(179, 166), S(105, 199), S( 70, 199) },
{ S(123, 92), S(145, 172), S( 81, 184), S( 31, 191) },
{ S( 88, 47), S(120, 121), S( 65, 116), S( 33, 131) },
{ S( 59, 11), S( 89, 59), S( 45, 73), S( -1, 78) }
}
};


constexpr S psq_table_pawns[6][8] =
{ // Pawn (asymmetric distribution)
{ S( 2, -8), S( 4, -6), S( 11, 9), S( 18, 5), S(16, 16), S( 21, 6), S( 9, -6), S( -3, -18) },
{ S(-9, -9), S(-15, -7), S( 11, -10), S( 15, 5), S(31, 2), S( 23, 3), S( 6, -8), S(-20, -5) },
{ S(-3, 7), S(-20, 1), S( 8, -8), S( 19, -2), S(39, -14), S( 17, -13), S( 2, -11), S( -5, -6) },
{ S(11, 12), S( -4, 6), S(-11, 2), S( 2, -6), S(11, -5), S( 0, -4), S(-12, 14), S( 5, 9) },
{ S( 3, 27), S(-11, 18), S( -6, 19), S( 22, 29), S(-8, 30), S( -5, 9), S(-14, 8), S(-11, 14) },
{ S(-7, -1), S( 6, -14), S( -2, 13), S(-11, 22), S( 4, 24), S(-14, 17), S( 10, 7), S( -9, 7) }
};


constexpr S imbalance_terms[][NUM_PIECE_TYPES] =
{ // Pawn Knight Bishop Rook Queen
{ S( 0, 0) }, // Pawn
{ S(14, 10), S(-5, -6) }, // Knight
{ S( 6, 7), S( 1, 2), S( 0, 0) }, // Bishop
{ S( 0, 0), S( 7, 4), S( 9, 8), S(-12, -11) }, // Rook
{ S( 0, 0), S( 9, 9), S(10, 7), S(-11, -13), S(0, 0) } // Queen
{ S( 0, 0) }, // Pawn
{ S(14, 10), S(-5, -6) }, // Knight
{ S( 6, 7), S( 1, 2), S( 0, 0) }, // Bishop
{ S( 0, 0), S( 7, 4), S( 9, 8), S(-12, -11) }, // Rook
{ S( 0, 0), S( 9, 9), S(10, 7), S(-11, -13), S(0, 0) } // Queen
};


constexpr MixedScore piece_square(PieceType piece, Square square, Turn turn)
namespace PSQT
{
// Correct piece position for table lookup
int sq_rank = (turn == WHITE) ? rank(square) : (7 - rank(square));
if (piece == PAWN)
return psq_table_pawns[sq_rank - 1][file(square)];
else
return psq_table[piece - 1][sq_rank][horizontal_distance(square)] / 2;
using FeatureType = int16_t;
static constexpr std::size_t NUM_FEATURES = 20480;

extern const FeatureType* psqt_data;

void init();

void load(std::string file);

void clean();
}


Score piece_square(PieceType piece, Square square, Turn turn, Square king_sq, Turn king_turn);
47 changes: 41 additions & 6 deletions src/Position.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -62,14 +62,15 @@ Board::Board()
Board::Board(std::string fen)
: m_hash(0),
m_material_hash(Zobrist::get_initial_material_hash()),
m_psq(0, 0),
m_phase(Phases::Total)
{
auto c = fen.cbegin();

// Default initialisation for board pieces
std::memset(m_board_pieces, PIECE_NONE, sizeof(m_board_pieces));
std::memset(m_piece_count, 0, sizeof(m_piece_count));
std::memset(m_psq, 0, sizeof(m_psq));
std::memset(m_king_sq, 0, sizeof(m_king_sq));

// Read position
Square square = SQUARE_A8;
Expand Down Expand Up @@ -120,6 +121,11 @@ Board::Board(std::string fen)
m_hash ^= Zobrist::get_ep_file(file(m_enpassant_square));

update_checkers();

m_king_sq[WHITE] = m_pieces[KING][WHITE].bitscan_forward();
m_king_sq[BLACK] = m_pieces[KING][BLACK].bitscan_forward();
regen_psqt(WHITE);
regen_psqt(BLACK);
}


Expand Down Expand Up @@ -213,6 +219,24 @@ void Board::update_checkers()
}


void Board::regen_psqt(Turn turn)
{
m_psq[turn] = 0;
for (PieceType p : { PAWN, KNIGHT, BISHOP, ROOK, QUEEN })
{
for (Turn t : { WHITE, BLACK })
{
Bitboard b = get_pieces(t, p);
while (b)
{
Square s = b.bitscan_forward_reset();
m_psq[turn] += piece_square(p, s, t, m_king_sq[turn], turn) * turn_to_color(t);
}
}
}
}


void Board::generate_moves(MoveList& list, MoveGenType type) const
{
if (m_turn == WHITE)
Expand Down Expand Up @@ -294,6 +318,13 @@ Board Board::make_move(Move move) const
result.move_piece(piece, m_turn, move.from(), move.to());
}

// After a king move, update PSQ tables
if (piece == KING)
{
result.m_king_sq[m_turn] = result.m_pieces[KING][m_turn].bitscan_forward();
result.regen_psqt(m_turn);
}

// Swap turns
result.m_turn = ~m_turn;
result.m_hash ^= Zobrist::get_black_move();
Expand Down Expand Up @@ -343,7 +374,7 @@ bool Board::is_valid() const
// Material and phase evaluation
uint8_t phase = Phases::Total;
MixedScore material(0, 0);
MixedScore psq(0, 0);
Score psq_sides[2] = { Score(0), Score(0) };
Hash material_hash = 0;
for (PieceType piece : { PAWN, KNIGHT, BISHOP, ROOK, QUEEN, KING })
for (Turn turn : { WHITE, BLACK })
Expand All @@ -355,14 +386,18 @@ bool Board::is_valid() const
phase -= bb.count() * Phases::Pieces[piece];
material_hash ^= Zobrist::get_piece_turn_square(piece, turn, bb.count());
while (bb)
psq += piece_square(piece, bb.bitscan_forward_reset(), turn) * turn_to_color(turn);
{
Square s = bb.bitscan_forward_reset();
psq_sides[WHITE] += piece_square(piece, s, turn, m_king_sq[WHITE], WHITE) * turn_to_color(turn);
psq_sides[BLACK] += piece_square(piece, s, turn, m_king_sq[BLACK], BLACK) * turn_to_color(turn);
}
}
MixedScore total_material = m_material[WHITE] - m_material[BLACK];
if (phase != m_phase)
return false;
if (material.middlegame() != total_material.middlegame() || material.endgame() != total_material.endgame())
return false;
if (psq.middlegame() != m_psq.middlegame() || psq.endgame() != m_psq.endgame())
if (psq_sides[WHITE] != m_psq[WHITE] || psq_sides[BLACK] != m_psq[BLACK])
return false;
if (material_hash != m_material_hash)
return false;
Expand Down Expand Up @@ -527,9 +562,9 @@ MixedScore Board::material(Turn turn) const
}


MixedScore Board::psq() const
Score Board::psq() const
{
return m_psq;
return m_psq[WHITE] + m_psq[BLACK];
}


Expand Down
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