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protonspring wants to merge 3 commits into from
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Simplify KPK classify #2485

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b839e11
simplify classify.
Jan 10, 2020
58aefcf
Merge branch 'master' into ps_classify3
Jan 12, 2020
dfa0d27
remove color from classify parm and use stm.
Jan 13, 2020
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56 changes: 25 additions & 31 deletions src/bitbase.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -43,8 +43,8 @@ namespace {
// bit 12: side to move (WHITE or BLACK)
// bit 13-14: white pawn file (from FILE_A to FILE_D)
// bit 15-17: white pawn RANK_7 - rank (from RANK_7 - RANK_7 to RANK_7 - RANK_2)
unsigned index(Color us, Square bksq, Square wksq, Square psq) {
return int(wksq) | (bksq << 6) | (us << 12) | (file_of(psq) << 13) | ((RANK_7 - rank_of(psq)) << 15);
unsigned index(Color stm, Square bksq, Square wksq, Square psq) {
return int(wksq) | (bksq << 6) | (stm << 12) | (file_of(psq) << 13) | ((RANK_7 - rank_of(psq)) << 15);
}

enum Result {
Expand All @@ -60,24 +60,21 @@ namespace {
KPKPosition() = default;
explicit KPKPosition(unsigned idx);
operator Result() const { return result; }
Result classify(const std::vector<KPKPosition>& db)
{ return us == WHITE ? classify<WHITE>(db) : classify<BLACK>(db); }
Result classify(const std::vector<KPKPosition>& db);

template<Color Us> Result classify(const std::vector<KPKPosition>& db);

Color us;
Color stm;
Square ksq[COLOR_NB], psq;
Result result;
};

} // namespace


bool Bitbases::probe(Square wksq, Square wpsq, Square bksq, Color us) {
bool Bitbases::probe(Square wksq, Square wpsq, Square bksq, Color stm) {

assert(file_of(wpsq) <= FILE_D);

unsigned idx = index(us, bksq, wksq, wpsq);
unsigned idx = index(stm, bksq, wksq, wpsq);
return KPKBitbase[idx / 32] & (1 << (idx & 0x1F));
}

Expand Down Expand Up @@ -110,36 +107,35 @@ namespace {

ksq[WHITE] = Square((idx >> 0) & 0x3F);
ksq[BLACK] = Square((idx >> 6) & 0x3F);
us = Color ((idx >> 12) & 0x01);
stm = Color ((idx >> 12) & 0x01);
psq = make_square(File((idx >> 13) & 0x3), Rank(RANK_7 - ((idx >> 15) & 0x7)));

// Check if two pieces are on the same square or if a king can be captured
if ( distance(ksq[WHITE], ksq[BLACK]) <= 1
|| ksq[WHITE] == psq
|| ksq[BLACK] == psq
|| (us == WHITE && (PawnAttacks[WHITE][psq] & ksq[BLACK])))
|| (stm == WHITE && (PawnAttacks[WHITE][psq] & ksq[BLACK])))
result = INVALID;

// Immediate win if a pawn can be promoted without getting captured
else if ( us == WHITE
else if ( stm == WHITE
&& rank_of(psq) == RANK_7
&& ksq[us] != psq + NORTH
&& ( distance(ksq[~us], psq + NORTH) > 1
|| (PseudoAttacks[KING][ksq[us]] & (psq + NORTH))))
&& ksq[stm] != psq + NORTH
&& ( distance(ksq[~stm], psq + NORTH) > 1
|| (PseudoAttacks[KING][ksq[stm]] & (psq + NORTH))))
result = WIN;

// Immediate draw if it is a stalemate or a king captures undefended pawn
else if ( us == BLACK
&& ( !(PseudoAttacks[KING][ksq[us]] & ~(PseudoAttacks[KING][ksq[~us]] | PawnAttacks[~us][psq]))
|| (PseudoAttacks[KING][ksq[us]] & psq & ~PseudoAttacks[KING][ksq[~us]])))
else if ( stm == BLACK
&& ( !(PseudoAttacks[KING][ksq[stm]] & ~(PseudoAttacks[KING][ksq[~stm]] | PawnAttacks[~stm][psq]))
|| (PseudoAttacks[KING][ksq[stm]] & psq & ~PseudoAttacks[KING][ksq[~stm]])))
result = DRAW;

// Position will be classified later
else
result = UNKNOWN;
}

template<Color Us>
Result KPKPosition::classify(const std::vector<KPKPosition>& db) {

// White to move: If one move leads to a position classified as WIN, the result
Expand All @@ -151,27 +147,25 @@ namespace {
// of the current position is DRAW. If all moves lead to positions classified
// as WIN, the position is classified as WIN, otherwise the current position is
// classified as UNKNOWN.

constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
constexpr Result Good = (Us == WHITE ? WIN : DRAW);
constexpr Result Bad = (Us == WHITE ? DRAW : WIN);
const Result Good = (stm == WHITE ? WIN : DRAW);
const Result Bad = (stm == WHITE ? DRAW : WIN);

Result r = INVALID;
Bitboard b = PseudoAttacks[KING][ksq[Us]];
Bitboard b = PseudoAttacks[KING][ksq[stm]];

while (b)
r |= Us == WHITE ? db[index(Them, ksq[Them] , pop_lsb(&b), psq)]
: db[index(Them, pop_lsb(&b), ksq[Them] , psq)];
r |= stm == WHITE ? db[index(BLACK, ksq[BLACK] , pop_lsb(&b), psq)]
: db[index(WHITE, pop_lsb(&b), ksq[WHITE], psq)];

if (Us == WHITE)
if (stm == WHITE)
{
if (rank_of(psq) < RANK_7) // Single push
r |= db[index(Them, ksq[Them], ksq[Us], psq + NORTH)];
r |= db[index(BLACK, ksq[BLACK], ksq[WHITE], psq + NORTH)];

if ( rank_of(psq) == RANK_2 // Double push
&& psq + NORTH != ksq[Us]
&& psq + NORTH != ksq[Them])
r |= db[index(Them, ksq[Them], ksq[Us], psq + NORTH + NORTH)];
&& psq + NORTH != ksq[WHITE]
&& psq + NORTH != ksq[BLACK])
r |= db[index(BLACK, ksq[BLACK], ksq[WHITE], psq + NORTH + NORTH)];
}

return result = r & Good ? Good : r & UNKNOWN ? UNKNOWN : Bad;
Expand Down