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https://github.com/sockspls/badfish
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Simplify bitbase.cpp
Use a std::vector to store positions and rearrange KPKPosition. No functional change. Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba
parent
733d0099b2
commit
f2950ae206
2 changed files with 90 additions and 105 deletions
193
src/bitbase.cpp
193
src/bitbase.cpp
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@ -18,12 +18,32 @@
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*/
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#include <cassert>
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#include <vector>
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#include "bitboard.h"
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#include "types.h"
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namespace {
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// The possible pawns squares are 24, the first 4 files and ranks from 2 to 7
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const unsigned IndexMax = 24*64*64*2; // wp_sq * wk_sq * bk_sq * stm = 196608
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// Each uint32_t stores results of 32 positions, one per bit
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uint32_t KPKBitbase[IndexMax / 32];
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// A KPK bitbase index is an integer in [0, IndexMax] range
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//
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// Information is mapped in this way
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//
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// bit 0: side to move (WHITE or BLACK)
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// bit 1- 6: black king square (from SQ_A1 to SQ_H8)
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// bit 7-12: white king square (from SQ_A1 to SQ_H8)
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// bit 13-14: white pawn file (from FILE_A to FILE_D)
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// bit 15-17: white pawn rank - 1 (from RANK_2 - 1 to RANK_7 - 1)
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unsigned index(Color stm, Square bksq, Square wksq, Square psq) {
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return stm + (bksq << 1) + (wksq << 7) + (file_of(psq) << 13) + ((rank_of(psq) - 1) << 15);
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}
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enum Result {
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INVALID = 0,
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UNKNOWN = 1,
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@ -35,153 +55,124 @@ namespace {
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struct KPKPosition {
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Result classify_leaf(int idx);
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Result classify(int idx, Result db[]);
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void classify_leaf(unsigned idx);
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Result classify(const std::vector<KPKPosition>& db)
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{ return stm == WHITE ? classify<WHITE>(db) : classify<BLACK>(db); }
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operator Result() const { return res; }
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private:
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template<Color Us> Result classify(const Result db[]) const;
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template<Color Us> Bitboard k_attacks() const
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{ return StepAttacksBB[KING][Us == WHITE ? wksq : bksq]; }
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template<Color Us> Bitboard k_attacks() const {
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return Us == WHITE ? StepAttacksBB[W_KING][wksq] : StepAttacksBB[B_KING][bksq];
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}
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template<Color Us> Result classify(const std::vector<KPKPosition>& db);
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Bitboard p_attacks() const { return StepAttacksBB[W_PAWN][psq]; }
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void decode_index(int idx);
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Square wksq, bksq, psq;
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Color stm;
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Square bksq, wksq, psq;
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Result res;
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};
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// The possible pawns squares are 24, the first 4 files and ranks from 2 to 7
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const int IndexMax = 2 * 24 * 64 * 64; // stm * wp_sq * wk_sq * bk_sq = 196608
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// Each uint32_t stores results of 32 positions, one per bit
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uint32_t KPKBitbase[IndexMax / 32];
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int index(Square wksq, Square bksq, Square psq, Color stm);
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}
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} // namespace
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uint32_t Bitbases::probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm) {
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bool Bitbases::probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm) {
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int idx = index(wksq, bksq, wpsq, stm);
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assert(file_of(wpsq) <= FILE_D);
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unsigned idx = index(stm, bksq, wksq, wpsq);
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return KPKBitbase[idx / 32] & (1 << (idx & 31));
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}
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void Bitbases::init_kpk() {
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Result* db = new Result[IndexMax]; // Avoid to hit stack limit on some platforms
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KPKPosition pos;
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int idx, bit, repeat = 1;
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unsigned idx, repeat = 1;
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std::vector<KPKPosition> db(IndexMax);
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// Initialize table with known win / draw positions
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// Initialize db with known win / draw positions
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for (idx = 0; idx < IndexMax; idx++)
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db[idx] = pos.classify_leaf(idx);
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db[idx].classify_leaf(idx);
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// Iterate until all positions are classified (30 cycles needed)
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while (repeat)
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for (repeat = idx = 0; idx < IndexMax; idx++)
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if (db[idx] == UNKNOWN && (db[idx] = pos.classify(idx, db)) != UNKNOWN)
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if (db[idx] == UNKNOWN && db[idx].classify(db) != UNKNOWN)
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repeat = 1;
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// Map 32 position results into one KPKBitbase[] entry
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for (idx = 0; idx < IndexMax / 32; idx++)
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for (bit = 0; bit < 32; bit++)
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if (db[32 * idx + bit] == WIN)
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KPKBitbase[idx] |= 1 << bit;
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delete [] db;
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// Map 32 results into one KPKBitbase[] entry
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for (idx = 0; idx < IndexMax; idx++)
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if (db[idx] == WIN)
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KPKBitbase[idx / 32] |= 1 << (idx & 31);
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}
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namespace {
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// A KPK bitbase index is an integer in [0, IndexMax] range
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//
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// Information is mapped in this way
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//
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// bit 0: side to move (WHITE or BLACK)
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// bit 1- 6: black king square (from SQ_A1 to SQ_H8)
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// bit 7-12: white king square (from SQ_A1 to SQ_H8)
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// bit 13-14: white pawn file (from FILE_A to FILE_D)
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// bit 15-17: white pawn rank - 1 (from RANK_2 - 1 to RANK_7 - 1)
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int index(Square w, Square b, Square p, Color c) {
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assert(file_of(p) <= FILE_D);
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return c + (b << 1) + (w << 7) + (file_of(p) << 13) + ((rank_of(p) - 1) << 15);
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}
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void KPKPosition::decode_index(int idx) {
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void KPKPosition::classify_leaf(unsigned idx) {
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stm = Color(idx & 1);
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bksq = Square((idx >> 1) & 63);
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wksq = Square((idx >> 7) & 63);
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bksq = Square((idx >> 1) & 0x3F);
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wksq = Square((idx >> 7) & 0x3F);
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psq = File((idx >> 13) & 3) | Rank((idx >> 15) + 1);
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}
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Result KPKPosition::classify_leaf(int idx) {
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decode_index(idx);
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// Check if two pieces are on the same square or if a king can be captured
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if ( wksq == psq || wksq == bksq || bksq == psq
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|| (k_attacks<WHITE>() & bksq)
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|| (stm == WHITE && (p_attacks() & bksq)))
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return INVALID;
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|| (stm == WHITE && (StepAttacksBB[PAWN][psq] & bksq)))
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res = INVALID;
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// The position is an immediate win if it is white to move and the white
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// pawn can be promoted without getting captured.
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if ( rank_of(psq) == RANK_7
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&& stm == WHITE
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&& wksq != psq + DELTA_N
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&& ( square_distance(bksq, psq + DELTA_N) > 1
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||(k_attacks<WHITE>() & (psq + DELTA_N))))
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return WIN;
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else if ( rank_of(psq) == RANK_7
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&& stm == WHITE
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&& wksq != psq + DELTA_N
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&& ( square_distance(bksq, psq + DELTA_N) > 1
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||(k_attacks<WHITE>() & (psq + DELTA_N))))
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res = WIN;
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// Check for known draw positions
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//
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// Case 1: Stalemate
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if ( stm == BLACK
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&& !(k_attacks<BLACK>() & ~(k_attacks<WHITE>() | p_attacks())))
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return DRAW;
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else if ( stm == BLACK
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&& !(k_attacks<BLACK>() & ~(k_attacks<WHITE>() | StepAttacksBB[PAWN][psq])))
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res = DRAW;
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// Case 2: King can capture undefended pawn
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if ( stm == BLACK
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&& (k_attacks<BLACK>() & psq & ~k_attacks<WHITE>()))
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return DRAW;
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else if ( stm == BLACK
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&& (k_attacks<BLACK>() & psq & ~k_attacks<WHITE>()))
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res = DRAW;
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// Case 3: Black king in front of white pawn
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if ( bksq == psq + DELTA_N
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&& rank_of(psq) < RANK_7)
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return DRAW;
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else if ( bksq == psq + DELTA_N
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&& rank_of(psq) < RANK_7)
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res = DRAW;
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// Case 4: White king in front of pawn and black has opposition
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if ( stm == WHITE
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&& wksq == psq + DELTA_N
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&& bksq == wksq + DELTA_N + DELTA_N
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&& rank_of(psq) < RANK_5)
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return DRAW;
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else if ( stm == WHITE
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&& wksq == psq + DELTA_N
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&& bksq == wksq + DELTA_N + DELTA_N
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&& rank_of(psq) < RANK_5)
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res = DRAW;
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// Case 5: Stalemate with rook pawn
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if ( bksq == SQ_A8
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&& file_of(psq) == FILE_A)
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return DRAW;
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else if ( bksq == SQ_A8
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&& file_of(psq) == FILE_A)
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res = DRAW;
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// Case 6: White king trapped on the rook file
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if ( file_of(wksq) == FILE_A
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&& file_of(psq) == FILE_A
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&& rank_of(wksq) > rank_of(psq)
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&& bksq == wksq + 2)
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return DRAW;
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else if ( file_of(wksq) == FILE_A
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&& file_of(psq) == FILE_A
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&& rank_of(wksq) > rank_of(psq)
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&& bksq == wksq + 2)
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res = DRAW;
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return UNKNOWN;
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else
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res = UNKNOWN;
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}
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template<Color Us>
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Result KPKPosition::classify(const Result db[]) const {
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Result KPKPosition::classify(const std::vector<KPKPosition>& db) {
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// White to Move: If one move leads to a position classified as RESULT_WIN,
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// the result of the current position is RESULT_WIN. If all moves lead to
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@ -198,35 +189,29 @@ namespace {
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while (b)
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{
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r |= Us == WHITE ? db[index(pop_lsb(&b), bksq, psq, BLACK)]
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: db[index(wksq, pop_lsb(&b), psq, WHITE)];
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r |= Us == WHITE ? db[index(BLACK, bksq, pop_lsb(&b), psq)]
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: db[index(WHITE, pop_lsb(&b), wksq, psq)];
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if (Us == WHITE && (r & WIN))
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return WIN;
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return res = WIN;
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if (Us == BLACK && (r & DRAW))
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return DRAW;
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return res = DRAW;
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}
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if (Us == WHITE && rank_of(psq) < RANK_7)
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{
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Square s = psq + DELTA_N;
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r |= db[index(wksq, bksq, s, BLACK)]; // Single push
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r |= db[index(BLACK, bksq, wksq, s)]; // Single push
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if (rank_of(s) == RANK_3 && s != wksq && s != bksq)
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r |= db[index(wksq, bksq, s + DELTA_N, BLACK)]; // Double push
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r |= db[index(BLACK, bksq, wksq, s + DELTA_N)]; // Double push
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if (r & WIN)
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return WIN;
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return res = WIN;
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}
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return r & UNKNOWN ? UNKNOWN : Us == WHITE ? DRAW : WIN;
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}
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Result KPKPosition::classify(int idx, Result db[]) {
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decode_index(idx);
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return stm == WHITE ? classify<WHITE>(db) : classify<BLACK>(db);
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return res = r & UNKNOWN ? UNKNOWN : Us == WHITE ? DRAW : WIN;
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}
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}
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@ -33,7 +33,7 @@ void print(Bitboard b);
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namespace Bitbases {
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void init_kpk();
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uint32_t probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm);
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bool probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm);
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}
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