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Slight simplification in scale factor computation

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[STC](http://tests.stockfishchess.org/tests/view/5b2614000ebc5902b8d17193)
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 17733 W: 3996 L: 3866 D: 9871

[LTC](http://tests.stockfishchess.org/tests/view/5b264d0f0ebc5902b8d17206)
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 55524 W: 9535 L: 9471 D: 36518

Use pawn count scaling also for opposite bishops endings with additional material, with a slope of 2 instead of 7. This simplifies slightly the code.

This PR is a functionally equivalent refactoring of the version which was submitted.

Four versions tried, 2 passed both STC and LTC. I picked the one which seemed more promising at LTC.

Slope 4 passed STC (-0.54 Elo), LTC not attempted
Slope 3 passed STC (+2.51 Elo), LTC (-0.44 Elo)
Slope 2 passed STC (+2.09 Elo), LTC (+0.04 Elo)
Slope 1 passed STC (+0.90 Elo), failed LTC (-3.40 Elo)

Bench: 4761613
This commit is contained in:
Stefano80 2018-06-20 05:24:24 +02:00 • committed by Stéphane Nicolet
parent a834bfe833
commit 9d219c07e4
1 changed files with 5 additions and 12 deletions
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17
src/evaluate.cpp
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@ -801,20 +801,13 @@ namespace {
// If scale is not already specific, scale down the endgame via general heuristics
if (sf == SCALE_FACTOR_NORMAL)
{
if (pos.opposite_bishops())
{
if ( pos.opposite_bishops()
&& pos.non_pawn_material(WHITE) == BishopValueMg
&& pos.non_pawn_material(BLACK) == BishopValueMg)
// Endgame with opposite-colored bishops and no other pieces is almost a draw
if ( pos.non_pawn_material(WHITE) == BishopValueMg
&& pos.non_pawn_material(BLACK) == BishopValueMg)
sf = 31;
// Endgame with opposite-colored bishops, but also other pieces. Still
// a bit drawish, but not as drawish as with only the two bishops.
else
sf = 46;
}
sf = 31;
else
sf = std::min(40 + 7 * pos.count<PAWN>(strongSide), sf);
sf = std::min(40 + (pos.opposite_bishops()? 2 : 7) * pos.count<PAWN>(strongSide), sf);
}
return ScaleFactor(sf);