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Scale down endgames with pawns on one or two adjacent files

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shane31
2014-06-25 16:01:00 -04:00
committed by Gary Linscott
parent ab580106fd
commit 6c9f4cf36f
3 changed files with 32 additions and 23 deletions
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41
src/evaluate.cpp
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@@ -197,6 +197,7 @@ namespace {
// scores, indexed by a calculated integer number.
Score KingDanger[128];
const int ScalePawnSpan[2] = { 38, 56 };
// apply_weight() weighs score 'v' by weight 'w' trying to prevent overflow
Score apply_weight(Score v, const Weight& w) {
@@ -726,29 +727,33 @@ namespace {
}
// Scale winning side if position is more drawish than it appears
ScaleFactor sf = eg_value(score) > VALUE_DRAW ? ei.mi->scale_factor(pos, WHITE)
: ei.mi->scale_factor(pos, BLACK);
Color strongSide = eg_value(score) > VALUE_DRAW ? WHITE : BLACK;
ScaleFactor sf = ei.mi->scale_factor(pos, strongSide);
// If we don't already have an unusual scale factor, check for opposite
// colored bishop endgames, and use a lower scale for those.
// If we don't already have an unusual scale factor, check for certain
// types of endgames, and use a lower scale for those.
if ( ei.mi->game_phase() < PHASE_MIDGAME
&& pos.opposite_bishops()
&& (sf == SCALE_FACTOR_NORMAL || sf == SCALE_FACTOR_ONEPAWN))
{
// Ignoring any pawns, do both sides only have a single bishop and no
// other pieces?
if ( pos.non_pawn_material(WHITE) == BishopValueMg
&& pos.non_pawn_material(BLACK) == BishopValueMg)
{
// Check for KBP vs KB with only a single pawn that is almost
// certainly a draw or at least two pawns.
bool one_pawn = (pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK) == 1);
sf = one_pawn ? ScaleFactor(8) : ScaleFactor(32);
if (pos.opposite_bishops()) {
// Ignoring any pawns, do both sides only have a single bishop and no
// other pieces?
if ( pos.non_pawn_material(WHITE) == BishopValueMg
&& pos.non_pawn_material(BLACK) == BishopValueMg)
{
// Check for KBP vs KB with only a single pawn that is almost
// certainly a draw or at least two pawns.
bool one_pawn = (pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK) == 1);
sf = one_pawn ? ScaleFactor(8) : ScaleFactor(32);
}
else
// Endgame with opposite-colored bishops, but also other pieces. Still
// a bit drawish, but not as drawish as with only the two bishops.
sf = ScaleFactor(50 * sf / SCALE_FACTOR_NORMAL);
} else if ( ei.pi->pawn_span(strongSide) <= 1 &&
!pos.pawn_passed(~strongSide, pos.king_square(~strongSide))) {
sf = ScaleFactor(ScalePawnSpan[ei.pi->pawn_span(strongSide)]);
}
else
// Endgame with opposite-colored bishops, but also other pieces. Still
// a bit drawish, but not as drawish as with only the two bishops.
sf = ScaleFactor(50 * sf / SCALE_FACTOR_NORMAL);
}
// Interpolate between a middlegame and a (scaled by 'sf') endgame score