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Variable null-move value based reduction

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Instead of a fixed reduction of ONE_PLY, now
Null move dynamic reduction based on value can
grow larger in case we are above beta of a value
much higher then PawnValueMg.

Note that now an eval returning VALUE_KNOWN_WIN
makes null search to drop in qsearch.

Passed both short TC:
LLR: 2.95 (-2.94,2.94) [-1.50,4.50]
Total: 26141 W: 4871 L: 4699 D: 16571

And long TC:
LLR: 2.97 (-2.94,2.94) [0.00,6.00]
Total: 33695 W: 5309 L: 5056 D: 23330

bench: 7356053
This commit is contained in:
Stefan Geschwentner 2014-01-24 21:52:56 +01:00 • committed by Marco Costalba
parent cf95a55d76
commit 074c7a3c30
1 changed files with 7 additions and 6 deletions
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13
src/search.cpp
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@ -628,12 +628,12 @@ namespace {
{
ss->currentMove = MOVE_NULL;
// Null move dynamic reduction based on depth
Depth R = 3 * ONE_PLY + depth / 4;
assert(eval - beta >= 0);
// Null move dynamic reduction based on value
if (eval - PawnValueMg > beta)
R += ONE_PLY;
// Null move dynamic reduction based on depth and value
Depth R = 3 * ONE_PLY
+ depth / (2 * ONE_PLY)
+ int(eval - beta) / PawnValueMg * ONE_PLY;
pos.do_null_move(st);
(ss+1)->skipNullMove = true;
@ -653,7 +653,8 @@ namespace {
// Do verification search at high depths
ss->skipNullMove = true;
Value v = search<NonPV>(pos, ss, alpha, beta, depth-R, false);
Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, alpha, beta, DEPTH_ZERO)
: search<NonPV>(pos, ss, alpha, beta, depth-R, false);
ss->skipNullMove = false;
if (v >= beta)