Value value_to_tt(Value v, int ply);
Value value_from_tt(Value v, int ply);
bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
+ bool ok_to_use_TT_PV(const TTEntry* tte, Depth depth, Value alpha, Value beta, int ply);
bool connected_threat(const Position& pos, Move m, Move threat);
Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
tte = TT.retrieve(posKey);
ttMove = tte ? tte->move() : MOVE_NONE;
- // At PV nodes, we don't use the TT for pruning, but only for move ordering.
- // This is to avoid problems in the following areas:
- //
- // * Repetition draw detection
- // * Fifty move rule detection
- // * Searching for a mate
- // * Printing of full PV line
- if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
+ // At PV nodes we check for exact scores within (alha, beta) range, while
+ // at non-PV nodes we check for and return a fail high/low. Biggest advantage
+ // at probing at PV nodes is to have a smooth experience in analysis mode.
+ if (!Root && tte && (PvNode ? ok_to_use_TT_PV(tte, depth, alpha, beta, ply) : ok_to_use_TT(tte, depth, beta, ply)))
{
TT.refresh(tte);
ss->bestMove = ttMove; // Can be MOVE_NONE
// ok_to_use_TT() returns true if a transposition table score
- // can be used at a given point in search.
+ // can be used at a given point in search. There are two versions
+ // one to be used in non-PV nodes and one in PV nodes where we look
+ // for an exact score that falls between (alha, beta) boundaries.
bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
|| ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
}
+ bool ok_to_use_TT_PV(const TTEntry* tte, Depth depth, Value alpha, Value beta, int ply) {
+
+ Value v = value_from_tt(tte->value(), ply);
+
+ return tte->depth() >= depth
+ && tte->type() == VALUE_TYPE_EXACT
+ && tte->move() != MOVE_NONE
+ && v < beta
+ && v > alpha;
+ }
+
// refine_eval() returns the transposition table score if
// possible otherwise falls back on static position evaluation.