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Shallow search to verify probcut

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Perform a preliminary shallow search to verify a probcut before doing
the normal "depth - 4 plies" search.

STC:
LLR: 4.73 (-2.94,2.94) [0.00,5.00]
Total: 36281 W: 8221 L: 7830 D: 20230
http://tests.stockfishchess.org/tests/view/5a921cb90ebc590297cc87f6

LTC:
LLR: 2.97 (-2.94,2.94) [0.00,5.00]
Total: 22907 W: 3954 L: 3738 D: 15215
http://tests.stockfishchess.org/tests/view/5a92672b0ebc590297cc8814

Happy to see something from Ethereal work for Stockfish :)

Bench: 5882274
This commit is contained in:
AndyGrant 2018-02-26 03:01:37 +01:00 • committed by Stéphane Nicolet
parent 7a03450bd9
commit 71cc01c2ef
1 changed files with 12 additions and 1 deletions
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13
src/search.cpp
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@ -742,7 +742,18 @@ namespace {
assert(depth >= 5 * ONE_PLY);
pos.do_move(move, st);
value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false);
// Perform a preliminary search at depth 1 to verify that the move holds.
// We will only do this search if the depth is not 5, thus avoiding two
// searches at depth 1 in a row.
if (depth != 5 * ONE_PLY)
value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, ONE_PLY, !cutNode, true);
// If the first search was skipped or was performed and held, perform
// the regular search.
if (depth == 5 * ONE_PLY || value >= rbeta)
value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false);
pos.undo_move(move);
if (value >= rbeta)
return value;