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Simplify bitbase.cpp

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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 2013-02-11 22:59:37 +01:00
parent 733d0099b2
commit f2950ae206
2 changed files with 90 additions and 105 deletions
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167
src/bitbase.cpp
View file

@ -18,12 +18,32 @@
*/ */
#include <cassert> #include <cassert>
#include <vector>
#include "bitboard.h" #include "bitboard.h"
#include "types.h" #include "types.h"
namespace { namespace {
// The possible pawns squares are 24, the first 4 files and ranks from 2 to 7
const unsigned IndexMax = 24*64*64*2; // wp_sq * wk_sq * bk_sq * stm = 196608
// Each uint32_t stores results of 32 positions, one per bit
uint32_t KPKBitbase[IndexMax / 32];
// A KPK bitbase index is an integer in [0, IndexMax] range
//
// Information is mapped in this way
//
// bit 0: side to move (WHITE or BLACK)
// bit 1- 6: black king square (from SQ_A1 to SQ_H8)
// bit 7-12: white king square (from SQ_A1 to SQ_H8)
// bit 13-14: white pawn file (from FILE_A to FILE_D)
// bit 15-17: white pawn rank - 1 (from RANK_2 - 1 to RANK_7 - 1)
unsigned index(Color stm, Square bksq, Square wksq, Square psq) {
return stm + (bksq << 1) + (wksq << 7) + (file_of(psq) << 13) + ((rank_of(psq) - 1) << 15);
}
enum Result { enum Result {
INVALID = 0, INVALID = 0,
UNKNOWN = 1, UNKNOWN = 1,
@ -35,153 +55,124 @@ namespace {
struct KPKPosition { struct KPKPosition {
Result classify_leaf(int idx); void classify_leaf(unsigned idx);
Result classify(int idx, Result db[]);
Result classify(const std::vector<KPKPosition>& db)
{ return stm == WHITE ? classify<WHITE>(db) : classify<BLACK>(db); }
operator Result() const { return res; }
private: private:
template<Color Us> Result classify(const Result db[]) const; template<Color Us> Bitboard k_attacks() const
{ return StepAttacksBB[KING][Us == WHITE ? wksq : bksq]; }
template<Color Us> Bitboard k_attacks() const { template<Color Us> Result classify(const std::vector<KPKPosition>& db);
return Us == WHITE ? StepAttacksBB[W_KING][wksq] : StepAttacksBB[B_KING][bksq];
}
Bitboard p_attacks() const { return StepAttacksBB[W_PAWN][psq]; }
void decode_index(int idx);
Square wksq, bksq, psq;
Color stm; Color stm;
Square bksq, wksq, psq;
Result res;
}; };
// The possible pawns squares are 24, the first 4 files and ranks from 2 to 7 } // namespace
const int IndexMax = 2 * 24 * 64 * 64; // stm * wp_sq * wk_sq * bk_sq = 196608
// Each uint32_t stores results of 32 positions, one per bit
uint32_t KPKBitbase[IndexMax / 32];
int index(Square wksq, Square bksq, Square psq, Color stm);
}
uint32_t Bitbases::probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm) { bool Bitbases::probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm) {
int idx = index(wksq, bksq, wpsq, stm); assert(file_of(wpsq) <= FILE_D);
unsigned idx = index(stm, bksq, wksq, wpsq);
return KPKBitbase[idx / 32] & (1 << (idx & 31)); return KPKBitbase[idx / 32] & (1 << (idx & 31));
} }
void Bitbases::init_kpk() { void Bitbases::init_kpk() {
Result* db = new Result[IndexMax]; // Avoid to hit stack limit on some platforms unsigned idx, repeat = 1;
KPKPosition pos; std::vector<KPKPosition> db(IndexMax);
int idx, bit, repeat = 1;
// Initialize table with known win / draw positions // Initialize db with known win / draw positions
for (idx = 0; idx < IndexMax; idx++) for (idx = 0; idx < IndexMax; idx++)
db[idx] = pos.classify_leaf(idx); db[idx].classify_leaf(idx);
// Iterate until all positions are classified (30 cycles needed) // Iterate until all positions are classified (30 cycles needed)
while (repeat) while (repeat)
for (repeat = idx = 0; idx < IndexMax; idx++) for (repeat = idx = 0; idx < IndexMax; idx++)
if (db[idx] == UNKNOWN && (db[idx] = pos.classify(idx, db)) != UNKNOWN) if (db[idx] == UNKNOWN && db[idx].classify(db) != UNKNOWN)
repeat = 1; repeat = 1;
// Map 32 position results into one KPKBitbase[] entry // Map 32 results into one KPKBitbase[] entry
for (idx = 0; idx < IndexMax / 32; idx++) for (idx = 0; idx < IndexMax; idx++)
for (bit = 0; bit < 32; bit++) if (db[idx] == WIN)
if (db[32 * idx + bit] == WIN) KPKBitbase[idx / 32] |= 1 << (idx & 31);
KPKBitbase[idx] |= 1 << bit;
delete [] db;
} }
namespace { namespace {
// A KPK bitbase index is an integer in [0, IndexMax] range void KPKPosition::classify_leaf(unsigned idx) {
//
// Information is mapped in this way
//
// bit 0: side to move (WHITE or BLACK)
// bit 1- 6: black king square (from SQ_A1 to SQ_H8)
// bit 7-12: white king square (from SQ_A1 to SQ_H8)
// bit 13-14: white pawn file (from FILE_A to FILE_D)
// bit 15-17: white pawn rank - 1 (from RANK_2 - 1 to RANK_7 - 1)
int index(Square w, Square b, Square p, Color c) {
assert(file_of(p) <= FILE_D);
return c + (b << 1) + (w << 7) + (file_of(p) << 13) + ((rank_of(p) - 1) << 15);
}
void KPKPosition::decode_index(int idx) {
stm = Color(idx & 1); stm = Color(idx & 1);
bksq = Square((idx >> 1) & 63); bksq = Square((idx >> 1) & 0x3F);
wksq = Square((idx >> 7) & 63); wksq = Square((idx >> 7) & 0x3F);
psq = File((idx >> 13) & 3) | Rank((idx >> 15) + 1); psq = File((idx >> 13) & 3) | Rank((idx >> 15) + 1);
}
Result KPKPosition::classify_leaf(int idx) {
decode_index(idx);
// Check if two pieces are on the same square or if a king can be captured // Check if two pieces are on the same square or if a king can be captured
if ( wksq == psq || wksq == bksq || bksq == psq if ( wksq == psq || wksq == bksq || bksq == psq
|| (k_attacks<WHITE>() & bksq) || (k_attacks<WHITE>() & bksq)
|| (stm == WHITE && (p_attacks() & bksq))) || (stm == WHITE && (StepAttacksBB[PAWN][psq] & bksq)))
return INVALID; res = INVALID;
// The position is an immediate win if it is white to move and the white // The position is an immediate win if it is white to move and the white
// pawn can be promoted without getting captured. // pawn can be promoted without getting captured.
if ( rank_of(psq) == RANK_7 else if ( rank_of(psq) == RANK_7
&& stm == WHITE && stm == WHITE
&& wksq != psq + DELTA_N && wksq != psq + DELTA_N
&& ( square_distance(bksq, psq + DELTA_N) > 1 && ( square_distance(bksq, psq + DELTA_N) > 1
||(k_attacks<WHITE>() & (psq + DELTA_N)))) ||(k_attacks<WHITE>() & (psq + DELTA_N))))
return WIN; res = WIN;
// Check for known draw positions // Check for known draw positions
// //
// Case 1: Stalemate // Case 1: Stalemate
if ( stm == BLACK else if ( stm == BLACK
&& !(k_attacks<BLACK>() & ~(k_attacks<WHITE>() | p_attacks()))) && !(k_attacks<BLACK>() & ~(k_attacks<WHITE>() | StepAttacksBB[PAWN][psq])))
return DRAW; res = DRAW;
// Case 2: King can capture undefended pawn // Case 2: King can capture undefended pawn
if ( stm == BLACK else if ( stm == BLACK
&& (k_attacks<BLACK>() & psq & ~k_attacks<WHITE>())) && (k_attacks<BLACK>() & psq & ~k_attacks<WHITE>()))
return DRAW; res = DRAW;
// Case 3: Black king in front of white pawn // Case 3: Black king in front of white pawn
if ( bksq == psq + DELTA_N else if ( bksq == psq + DELTA_N
&& rank_of(psq) < RANK_7) && rank_of(psq) < RANK_7)
return DRAW; res = DRAW;
// Case 4: White king in front of pawn and black has opposition // Case 4: White king in front of pawn and black has opposition
if ( stm == WHITE else if ( stm == WHITE
&& wksq == psq + DELTA_N && wksq == psq + DELTA_N
&& bksq == wksq + DELTA_N + DELTA_N && bksq == wksq + DELTA_N + DELTA_N
&& rank_of(psq) < RANK_5) && rank_of(psq) < RANK_5)
return DRAW; res = DRAW;
// Case 5: Stalemate with rook pawn // Case 5: Stalemate with rook pawn
if ( bksq == SQ_A8 else if ( bksq == SQ_A8
&& file_of(psq) == FILE_A) && file_of(psq) == FILE_A)
return DRAW; res = DRAW;
// Case 6: White king trapped on the rook file // Case 6: White king trapped on the rook file
if ( file_of(wksq) == FILE_A else if ( file_of(wksq) == FILE_A
&& file_of(psq) == FILE_A && file_of(psq) == FILE_A
&& rank_of(wksq) > rank_of(psq) && rank_of(wksq) > rank_of(psq)
&& bksq == wksq + 2) && bksq == wksq + 2)
return DRAW; res = DRAW;
return UNKNOWN; else
res = UNKNOWN;
} }
template<Color Us> template<Color Us>
Result KPKPosition::classify(const Result db[]) const { Result KPKPosition::classify(const std::vector<KPKPosition>& db) {
// White to Move: If one move leads to a position classified as RESULT_WIN, // White to Move: If one move leads to a position classified as RESULT_WIN,
// the result of the current position is RESULT_WIN. If all moves lead to // the result of the current position is RESULT_WIN. If all moves lead to
@ -198,35 +189,29 @@ namespace {
while (b) while (b)
{ {
r |= Us == WHITE ? db[index(pop_lsb(&b), bksq, psq, BLACK)] r |= Us == WHITE ? db[index(BLACK, bksq, pop_lsb(&b), psq)]
: db[index(wksq, pop_lsb(&b), psq, WHITE)]; : db[index(WHITE, pop_lsb(&b), wksq, psq)];
if (Us == WHITE && (r & WIN)) if (Us == WHITE && (r & WIN))
return WIN; return res = WIN;
if (Us == BLACK && (r & DRAW)) if (Us == BLACK && (r & DRAW))
return DRAW; return res = DRAW;
} }
if (Us == WHITE && rank_of(psq) < RANK_7) if (Us == WHITE && rank_of(psq) < RANK_7)
{ {
Square s = psq + DELTA_N; Square s = psq + DELTA_N;
r |= db[index(wksq, bksq, s, BLACK)]; // Single push r |= db[index(BLACK, bksq, wksq, s)]; // Single push
if (rank_of(s) == RANK_3 && s != wksq && s != bksq) if (rank_of(s) == RANK_3 && s != wksq && s != bksq)
r |= db[index(wksq, bksq, s + DELTA_N, BLACK)]; // Double push r |= db[index(BLACK, bksq, wksq, s + DELTA_N)]; // Double push
if (r & WIN) if (r & WIN)
return WIN; return res = WIN;
} }
return r & UNKNOWN ? UNKNOWN : Us == WHITE ? DRAW : WIN; return res = r & UNKNOWN ? UNKNOWN : Us == WHITE ? DRAW : WIN;
}
Result KPKPosition::classify(int idx, Result db[]) {
decode_index(idx);
return stm == WHITE ? classify<WHITE>(db) : classify<BLACK>(db);
} }
} }

2
src/bitboard.h
View file

@ -33,7 +33,7 @@ void print(Bitboard b);
namespace Bitbases { namespace Bitbases {
void init_kpk(); void init_kpk();
uint32_t probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm); bool probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm);
} }