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Weight backward-ness of a pawn

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Because not all backward pawns are the same ;-) if the
blocking enemy pawn is near then our pawn is more backward
than another whose enemy pawn is far away so that can advance
for some sqaures.

After 2925 games at 30"+0 on my QUAD
Mod vs Orig +602 =1745 -578 +3 ELO

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2010-07-19 08:56:14 +02:00
parent 6aef4429fd
commit 26a8b84417
1 changed files with 8 additions and 2 deletions
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10
src/pawns.cpp
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@ -183,7 +183,7 @@ Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
Square s;
File f;
Rank r;
int bonus;
int bonus, backwardWeight;
bool passed, isolated, doubled, opposed, chain, backward, candidate;
Score value = make_score(0, 0);
const Square* ptr = pos.piece_list_begin(Us, PAWN);
@ -227,6 +227,7 @@ Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
// Test for backward pawn
//
backward = false;
backwardWeight = 6;
// If the pawn is passed, isolated, or member of a pawn chain
// it cannot be backward. If can capture an enemy pawn or if
@ -245,7 +246,12 @@ Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
// Note that we are sure to find something because pawn is not passed
// nor isolated, so loop is potentially infinite, but it isn't.
while (!(b & (ourPawns | theirPawns)))
{
Us == WHITE ? b <<= 8 : b >>= 8;
backwardWeight--;
}
assert(backwardWeight > 0);
// The friendly pawn needs to be at least two ranks closer than the enemy
// pawn in order to help the potentially backward pawn advance.
@ -282,7 +288,7 @@ Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
if (backward)
{
value -= BackwardPawnPenalty[f];
value -= backwardWeight * BackwardPawnPenalty[f] / 4;
if (!opposed)
value -= BackwardPawnPenalty[f] / 2;
}