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Code Issues Releases Wiki Activity

Drop the lever condition for backwards

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We can view the patch version as adding some "undermining bonus" for
level pawns, when the defending side can not easily avoid the exchange
by advancing her pawn.

• Case 1) White b2,c3, Black a3,b3:
          Black is breaking through, b2 deserves a penalty

• Case 2) White b2,c3, Black a3,c4:
          if b2xa3 then White ends up with a weak pawn on a3
          and probably a weak pawn on c3 too.

In either case, White can still not safely play b2-b3 and make a
phalanx with c3, which is the essence of a backward pawn definition.

Passed STC in SPRT[0, 4]:
LLR: -2.96 (-2.94,2.94) [0.00,4.00]
Total: 131169 W: 26523 L: 26199 D: 78447
http://tests.stockfishchess.org/tests/view/5aefa4d50ebc5902a409a151
ELO 1.19 [-0.38,2.88] (95%)

Passed LTC in SPRT[-3, 1]:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 24824 W: 3732 L: 3617 D: 17475
http://tests.stockfishchess.org/tests/view/5af04d3f0ebc5902a88b2e55
ELO 1.27 [-1.21,3.70] (95%)

Closes https://github.com/official-stockfish/Stockfish/pull/1584

How to continue from there?

There were some promising tests a couple of months ago about adding
a lever condition for king danger in evaluate.cpp, maybe it would
be time to re-try this after all the recent changes in pawns.cpp

Bench: 4773882
This commit is contained in:
Alain SAVARD 2018-05-08 11:00:51 +02:00 • committed by Stéphane Nicolet
parent 8d1625d6df
commit 6634f41ac9
2 changed files with 11 additions and 5 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

10
src/movepick.h
View file

@ -117,8 +117,14 @@ public:
MovePicker(const MovePicker&) = delete;
MovePicker& operator=(const MovePicker&) = delete;
MovePicker(const Position&, Move, Value, const CapturePieceToHistory*);
MovePicker(const Position&, Move, Depth, const ButterflyHistory*, const CapturePieceToHistory*, Square);
MovePicker(const Position&, Move, Depth, const ButterflyHistory*, const CapturePieceToHistory*, const PieceToHistory**, Move, Move*);
MovePicker(const Position&, Move, Depth, const ButterflyHistory*,
const CapturePieceToHistory*,
Square);
MovePicker(const Position&, Move, Depth, const ButterflyHistory*,
const CapturePieceToHistory*,
const PieceToHistory**,
Move,
Move*);
Move next_move(bool skipQuiets = false);
private:

4
src/pawns.cpp
View file

@ -118,7 +118,7 @@ namespace {
// A pawn is backward when it is behind all pawns of the same color
// on the adjacent files and cannot be safely advanced.
backward = !lever && !(ourPawns & pawn_attack_span(Them, s + Up))
backward = !(ourPawns & pawn_attack_span(Them, s + Up))
&& (stoppers & (leverPush | (s + Up)));
// Passed pawns will be properly scored in evaluation because we need
@ -223,7 +223,7 @@ Value Entry::evaluate_shelter(const Position& pos, Square ksq) {
Value safety = (ourPawns & file_bb(ksq)) ? Value(5) : Value(-5);
if ((shift<Down>(theirPawns) & (FileABB | FileHBB) & BlockRanks) & ksq)
if (shift<Down>(theirPawns) & (FileABB | FileHBB) & BlockRanks & ksq)
safety += 374;
File center = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));