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Use full evaluation in null search

Browse source 
This is an important design change because we know
compute evaluation in each node.

This is a 2.0 type change!

After 977 games at 1+0

Mod vs Orig +236 =538 -202 51.74%  +12 ELO

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2010-01-05 09:57:48 +01:00
parent e2e360fcbc
commit dba072c449
1 changed files with 21 additions and 17 deletions
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38
src/search.cpp
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@ -1341,7 +1341,7 @@ namespace {
const TTEntry* tte;
Move ttMove, move;
Depth ext, newDepth;
Value approximateEval, nullValue, value, futilityValue, futilityValueScaled;
Value staticValue, nullValue, value, futilityValue, futilityValueScaled;
bool isCheck, useFutilityPruning, singleEvasion, moveIsCheck, captureOrPromotion, dangerous;
bool mateThreat = false;
int moveCount = 0;
@ -1385,8 +1385,24 @@ namespace {
return value_from_tt(tte->value(), ply);
}
approximateEval = refine_eval(tte, quick_evaluate(pos), ply);
isCheck = pos.is_check();
ei.futilityMargin = Value(0); // Manually initialize futilityMargin
// Evaluate the position statically
if (isCheck)
staticValue = quick_evaluate(pos);
else if (tte && (tte->type() & VALUE_TYPE_EVAL))
staticValue = value_from_tt(tte->value(), ply);
else
staticValue = evaluate(pos, ei, threadID);
// Calculate depth dependant futility pruning parameters
const int FutilityMoveCountMargin = 3 + (1 << (3 * int(depth) / 8));
const int FutilityValueMargin = 112 * bitScanReverse32(int(depth) * int(depth) / 2);
// Enhance position with TT value if possible
futilityValue = staticValue + FutilityValueMargin;
staticValue = refine_eval(tte, staticValue, ply);
// Null move search
if ( allowNullmove
@ -1394,7 +1410,7 @@ namespace {
&& !isCheck
&& !value_is_mate(beta)
&& ok_to_do_nullmove(pos)
&& approximateEval >= beta - NullMoveMargin)
&& staticValue >= beta - NullMoveMargin)
{
ss[ply].currentMove = MOVE_NULL;
@ -1404,7 +1420,7 @@ namespace {
int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
// Null move dynamic reduction based on value
if (approximateEval - beta > PawnValueMidgame)
if (staticValue - beta > PawnValueMidgame)
R++;
nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
@ -1440,7 +1456,7 @@ namespace {
// Null move search not allowed, try razoring
else if ( !value_is_mate(beta)
&& depth < RazorDepth
&& approximateEval < beta - RazorApprMargins[int(depth) - 2]
&& staticValue < beta - RazorApprMargins[int(depth) - 2]
&& ss[ply - 1].currentMove != MOVE_NULL
&& ttMove == MOVE_NONE
&& !pos.has_pawn_on_7th(pos.side_to_move()))
@ -1464,17 +1480,8 @@ namespace {
// to search all moves.
MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
CheckInfo ci(pos);
futilityValue = VALUE_NONE;
useFutilityPruning = depth < SelectiveDepth && !isCheck;
// Calculate depth dependant futility pruning parameters
const int FutilityMoveCountMargin = 3 + (1 << (3 * int(depth) / 8));
const int FutilityValueMargin = 112 * bitScanReverse32(int(depth) * int(depth) / 2);
// Avoid calling evaluate() if we already have the score in TT
if (tte && (tte->type() & VALUE_TYPE_EVAL))
futilityValue = value_from_tt(tte->value(), ply) + FutilityValueMargin;
// Loop through all legal moves until no moves remain or a beta cutoff occurs
while ( bestValue < beta
&& (move = mp.get_next_move()) != MOVE_NONE
@ -1532,9 +1539,6 @@ namespace {
continue;
// Value based pruning
if (futilityValue == VALUE_NONE)
futilityValue = evaluate(pos, ei, threadID) + FutilityValueMargin;
futilityValueScaled = futilityValue - moveCount * IncrementalFutilityMargin;
if (futilityValueScaled < beta)