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Drop alpha and beta in search

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Useless because they are always WDLLoss and WDLWin.
This commit is contained in:
Marco Costalba 2016-06-03 08:01:17 +02:00
parent 9d088003f4
commit f71e21e3af
1 changed files with 19 additions and 17 deletions
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36
src/syzygy/tbprobe.cpp
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@ -1174,9 +1174,9 @@ T probe_table(const Position& pos, ProbeState* result, WDLScore wdl = WDLDraw) {
// where the best move is an ep-move (even if losing). So in all these cases set // where the best move is an ep-move (even if losing). So in all these cases set
// the state to ZEROING_BEST_MOVE. // the state to ZEROING_BEST_MOVE.
template<bool CheckZeroingMoves = false> template<bool CheckZeroingMoves = false>
WDLScore search(Position& pos, WDLScore alpha, WDLScore beta, ProbeState* result) { WDLScore search(Position& pos, ProbeState* result) {
WDLScore value; WDLScore value, bestValue = WDLLoss;
StateInfo st; StateInfo st;
CheckInfo ci(pos); CheckInfo ci(pos);
@ -1192,20 +1192,22 @@ WDLScore search(Position& pos, WDLScore alpha, WDLScore beta, ProbeState* result
moveCount++; moveCount++;
pos.do_move(move, st, pos.gives_check(move, ci)); pos.do_move(move, st, pos.gives_check(move, ci));
value = -search(pos, -beta, -alpha, result); value = -search(pos, result);
pos.undo_move(move); pos.undo_move(move);
if (*result == FAIL) if (*result == FAIL)
return WDLDraw; return WDLDraw;
if (value >= beta) if (value > bestValue)
{ {
*result = ZEROING_BEST_MOVE; // Winning DTZ-zeroing move bestValue = value;
return value;
}
if (value > alpha) if (value >= WDLWin)
alpha = value; {
*result = ZEROING_BEST_MOVE; // Winning DTZ-zeroing move
return value;
}
}
} }
// In case we have already searched all the legal moves we don't have to probe // In case we have already searched all the legal moves we don't have to probe
@ -1217,7 +1219,7 @@ WDLScore search(Position& pos, WDLScore alpha, WDLScore beta, ProbeState* result
bool noMoreMoves = (moveCount && moveCount == totalCount); bool noMoreMoves = (moveCount && moveCount == totalCount);
if (noMoreMoves) if (noMoreMoves)
value = alpha; value = bestValue;
else else
{ {
value = probe_table<WDLEntry>(pos, result); value = probe_table<WDLEntry>(pos, result);
@ -1226,10 +1228,10 @@ WDLScore search(Position& pos, WDLScore alpha, WDLScore beta, ProbeState* result
return WDLDraw; return WDLDraw;
} }
// Here alpha stores the best value of the ply-1 search, note that in case // DTZ stores a "don't care" value if bestValue is a win
// we have already searched all the possible moves alpha == value. if (bestValue >= value)
if (alpha >= value) return *result = ( bestValue > WDLDraw
return *result = (alpha > WDLDraw || noMoreMoves ? ZEROING_BEST_MOVE : OK), alpha; || noMoreMoves ? ZEROING_BEST_MOVE : OK), bestValue;
return *result = OK, value; return *result = OK, value;
} }
@ -1377,7 +1379,7 @@ void Tablebases::init(const std::string& paths) {
WDLScore Tablebases::probe_wdl(Position& pos, ProbeState* result) { WDLScore Tablebases::probe_wdl(Position& pos, ProbeState* result) {
*result = OK; *result = OK;
return search(pos, WDLLoss, WDLWin, result); return search(pos, result);
} }
// Probe the DTZ table for a particular position. // Probe the DTZ table for a particular position.
@ -1408,7 +1410,7 @@ WDLScore Tablebases::probe_wdl(Position& pos, ProbeState* result) {
int Tablebases::probe_dtz(Position& pos, ProbeState* result) { int Tablebases::probe_dtz(Position& pos, ProbeState* result) {
*result = OK; *result = OK;
WDLScore wdl = search<true>(pos, WDLLoss, WDLWin, result); WDLScore wdl = search<true>(pos, result);
if (*result == FAIL) if (*result == FAIL)
return 0; return 0;
@ -1445,7 +1447,7 @@ int Tablebases::probe_dtz(Position& pos, ProbeState* result) {
// otherwise we will get the dtz of the next move sequence. Search the // otherwise we will get the dtz of the next move sequence. Search the
// position after the move to get the score sign (because even in a // position after the move to get the score sign (because even in a
// winning position we could make a losing capture or going for a draw). // winning position we could make a losing capture or going for a draw).
dtz = zeroing ? -zeroing_move_dtz(search(pos, WDLLoss, WDLWin, result)) dtz = zeroing ? -zeroing_move_dtz(search(pos, result))
: -probe_dtz(pos, result); : -probe_dtz(pos, result);
pos.undo_move(move); pos.undo_move(move);