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Better document search stop condition

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Handling a stop or a cutoff in the search is
a tricky business, so better document this
difficult part of the code.

No functional change.
This commit is contained in:
Marco Costalba
2014-05-01 08:28:49 +02:00
parent 626dc8a03b
commit da91a34c09
1 changed files with 15 additions and 11 deletions
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26
src/search.cpp
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@@ -936,12 +936,11 @@ moves_loop: // When in check and at SpNode search starts from here
alpha = splitPoint->alpha;
}
// Finished searching the move. If Signals.stop is true, the search
// was aborted because the user interrupted the search or because we
// ran out of time. In this case, the return value of the search cannot
// be trusted, and we don't update the best move and/or PV.
// Finished searching the move. If a stop or a cutoff occurred, the return
// value of the search cannot be trusted, and we return immediately without
// updating best move, PV and TT.
if (Signals.stop || thisThread->cutoff_occurred())
return value; // To avoid returning VALUE_INFINITE
return VALUE_DRAW;
if (RootNode)
{
@@ -994,7 +993,7 @@ moves_loop: // When in check and at SpNode search starts from here
&& Threads.available_slave(thisThread)
&& thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
{
assert(bestValue < beta);
assert(bestValue > -VALUE_INFINITE && bestValue < beta);
thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
depth, moveCount, &mp, NT, cutNode);
@@ -1006,13 +1005,18 @@ moves_loop: // When in check and at SpNode search starts from here
if (SpNode)
return bestValue;
// Following condition would detect a stop or a cutoff set only after move
// loop has been completed. But in this case bestValue is valid because we
// have fully searched our subtree, and we can anyhow save the result in TT.
/*
if (Signals.stop || thisThread->cutoff_occurred())
return VALUE_DRAW;
*/
// Step 20. Check for mate and stalemate
// All legal moves have been searched and if there are no legal moves, it
// must be mate or stalemate. Note that we can have a false positive in
// case of Signals.stop or thread.cutoff_occurred() are set, but this is
// harmless because return value is discarded anyhow in the parent nodes.
// If we are in a singular extension search then return a fail low score.
// A split node has at least one move - the one tried before to be split.
// must be mate or stalemate. If we are in a singular extension search then
// return a fail low score.
if (!moveCount)
return excludedMove ? alpha
: inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];