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Reintroduce depth 2 razoring (with additional margin)

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The first depth 2 margin triggers the verification quiescence search.
This qsearch() result has to be better then the second lower margin,
so we only skip the razoring when the qsearch gives a significant
improvement.

Passed STC:
LLR: 2.95 (-2.94,2.94) [0.00,5.00]
Total: 32133 W: 7395 L: 7101 D: 17637
http://tests.stockfishchess.org/tests/view/5a93198b0ebc590297cc8942

Passed LTC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 17382 W: 3002 L: 2809 D: 11571
http://tests.stockfishchess.org/tests/view/5a93b18c0ebc590297cc89c2

This Elo-gaining version was further simplified following a suggestion
of Marco Costalba:

STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 15553 W: 3505 L: 3371 D: 8677
http://tests.stockfishchess.org/tests/view/5a964be90ebc590297cc8cc4

LTC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 13253 W: 2270 L: 2137 D: 8846
http://tests.stockfishchess.org/tests/view/5a9658880ebc590297cc8cca

How to continue after this patch?

Reformating the razoring code (step 7 in search()) to unify the
depth 1 and depth 2 treatements seems quite possible, this could
possibly lead to more simplifications.

Bench: 5765806
This commit is contained in:
Tom Vijlbrief 2018-02-28 13:41:24 +01:00 • committed by Stéphane Nicolet
parent 59d10374ca
commit 94abc2a0cf
1 changed files with 17 additions and 5 deletions
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22
src/search.cpp
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@ -66,8 +66,9 @@ namespace {
const int SkipSize[] = { 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4 };
const int SkipPhase[] = { 0, 1, 0, 1, 2, 3, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6, 7 };
// Razoring and futility margins
const int RazorMargin = 590;
// Razor and futility margins
const int RazorMargin1 = 590;
const int RazorMargin2 = 604;
Value futility_margin(Depth d) { return Value(150 * d / ONE_PLY); }
// Futility and reductions lookup tables, initialized at startup
@ -680,9 +681,20 @@ namespace {
// Step 7. Razoring (skipped when in check)
if ( !PvNode
&& depth <= ONE_PLY
&& eval + RazorMargin <= alpha)
return qsearch<NonPV, false>(pos, ss, alpha, alpha+1);
&& depth <= ONE_PLY)
{
if (eval + RazorMargin1 <= alpha)
return qsearch<NonPV, false>(pos, ss, alpha, alpha+1);
}
else if ( !PvNode
&& depth <= 2 * ONE_PLY
&& eval + RazorMargin2 <= alpha)
{
Value ralpha = alpha - RazorMargin2;
Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1);
if (v <= ralpha)
return v;
}
// Step 8. Futility pruning: child node (skipped when in check)
if ( !rootNode