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Simplify BlockedByKing in pawn storms

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This patch is non-functional. Current master does four operations to determine
whether an enemy pawn on this file is blocked by the king or not

```
f == file_of(ksq) && rkThem == relative_rank(Us, ksq) + 1 )
```

By adding a direction (based on the template color), this is reduced to two
operations. This works because b is limited to enemy pawns that are ahead of
the king and on the current file.

```
shift<Down>(b) & ksq
```

I've added a line of code, but the number of executing instructions is reduced
(I think). I'm not sure if this counts as a simplification, but it should
theoretically be a little faster (barely). The code line length is also reduced
making it a little easier to read.

Closes https://github.com/official-stockfish/Stockfish/pull/1552

No functional change.
This commit is contained in:
protonspring 2018-04-18 20:03:37 +02:00 • committed by Stéphane Nicolet
parent 73e8daa150
commit f7cc0026e3
1 changed files with 5 additions and 4 deletions
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9
src/pawns.cpp
View file

@ -236,7 +236,8 @@ Entry* probe(const Position& pos) {
template<Color Us>
Value Entry::shelter_storm(const Position& pos, Square ksq) {
constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
enum { BlockedByKing, Unopposed, BlockedByPawn, Unblocked };
@ -257,9 +258,9 @@ Value Entry::shelter_storm(const Position& pos, Square ksq) {
int d = std::min(f, ~f);
safety -= ShelterWeakness[f == file_of(ksq)][d][rkUs]
+ StormDanger
[f == file_of(ksq) && rkThem == relative_rank(Us, ksq) + 1 ? BlockedByKing :
rkUs == RANK_1 ? Unopposed :
rkThem == rkUs + 1 ? BlockedByPawn : Unblocked]
[(shift<Down>(b) & ksq) ? BlockedByKing :
rkUs == RANK_1 ? Unopposed :
rkThem == (rkUs + 1) ? BlockedByPawn : Unblocked]
[d][rkThem];
}