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Fix (zugzwang) verification to be shallower then null search

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Currently starting from depth 12*OnePly on we have a verification
search deeper then the null search.

Note that, although reduction is R we start from one ply less then
null search, so actually we reach a depth that is OnePly shallower
then null search.

After 1130 games at 1'+0 on QUAD
Mod vs Orig +202 =756 -172  +9 ELO

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba
2010-07-11 07:52:05 +01:00
parent 00e86078a5
commit a47a7dadeb
1 changed files with 2 additions and 2 deletions
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4
src/search.cpp
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@@ -1203,12 +1203,12 @@ namespace {
if (nullValue >= value_mate_in(PLY_MAX))
nullValue = beta;
// Do zugzwang verification search at high depths
if (depth < 6 * OnePly)
return nullValue;
// Do verification search at high depths
ss->skipNullMove = true;
Value v = search<NonPV>(pos, ss, alpha, beta, depth-5*OnePly, ply);
Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*OnePly, ply);
ss->skipNullMove = false;
if (v >= beta)