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Cache evaluation score in qsearch

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Instead of just drop evaluation score after stand pat
logic save it in TT so to be reused if the same position
occurs again.

Note that we NEVER use the cached value apart to avoid an
evaluation call, in particulary we never return to caller
after a succesful tt hit.

To accomodate this a new value type VALUE_TYPE_EVAL has been
introduced so that ok_to_use_TT() always returns false.

With this patch we cut about 15% of total evaluation calls.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba
2009-03-24 15:48:14 +01:00
parent 1c087dd806
commit 5a0581498c
6 changed files with 37 additions and 16 deletions
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31
src/search.cpp
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@@ -1434,18 +1434,38 @@ namespace {
return VALUE_DRAW;
// Transposition table lookup, only when not in PV
TTEntry* tte = NULL;
bool pvNode = (beta - alpha != 1);
if (!pvNode)
{
const TTEntry* tte = TT.retrieve(pos);
tte = TT.retrieve(pos);
if (tte && ok_to_use_TT(tte, depth, beta, ply))
{
assert(tte->type() != VALUE_TYPE_EVAL);
return value_from_tt(tte->value(), ply);
}
}
// Evaluate the position statically
EvalInfo ei;
Value staticValue;
bool isCheck = pos.is_check();
Value staticValue = (isCheck ? -VALUE_INFINITE : evaluate(pos, ei, threadID));
if (isCheck)
staticValue = -VALUE_INFINITE;
else if (tte && tte->type() == VALUE_TYPE_EVAL)
{
// Use the cached evaluation score if possible
assert(tte->value() == evaluate(pos, ei, threadID));
assert(ei.futilityMargin == Value(0));
staticValue = tte->value();
ei.futilityMargin = Value(0); // manually initialize futilityMargin
}
else
staticValue = evaluate(pos, ei, threadID);
if (ply == PLY_MAX - 1)
return evaluate(pos, ei, threadID);
@@ -1460,6 +1480,11 @@ namespace {
TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE, VALUE_TYPE_EXACT);
return bestValue;
}
else if (!isCheck && !tte && ei.futilityMargin == 0)
{
// Store the score to avoid a future costly evaluation() call
TT.store(pos, value_to_tt(bestValue, ply), Depth(-127*OnePly), MOVE_NONE, VALUE_TYPE_EVAL);
}
if (bestValue > alpha)
alpha = bestValue;
@@ -1467,7 +1492,7 @@ namespace {
// Initialize a MovePicker object for the current position, and prepare
// to search the moves. Because the depth is <= 0 here, only captures,
// queen promotions and checks (only if depth == 0) will be generated.
MovePicker mp = MovePicker(pos, pvNode, MOVE_NONE, EmptySearchStack, depth, isCheck ? NULL : &ei);
MovePicker mp = MovePicker(pos, pvNode, MOVE_NONE, EmptySearchStack, depth);
Move move;
int moveCount = 0;
Bitboard dcCandidates = mp.discovered_check_candidates();