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.
template<Color Us>
Value Entry::shelter_storm(const Position& pos, Square ksq) {
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 };
enum { BlockedByKing, Unopposed, BlockedByPawn, Unblocked };
int d = std::min(f, ~f);
safety -= ShelterWeakness[f == file_of(ksq)][d][rkUs]
+ StormDanger
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]