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Correct a bug introduced by Stéphane in the previous patch.

Browse source 
When we are using the "Bitboard + Square" overloaded operators,
the compiler uses the interpediate SquareBB[s] to transform the
square into a Bitboard, and then calculate the result.

For instance, the following code:

```
   b = pos.pieces(Us, PAWN) & s
```

generates in fact the code:

```
   b = pos.pieces(Us, PAWN) & SquareBB[s]`
```

The bug introduced by Stéphane in the previous patch was the
use of `b = pos.pieces(Us, PAWN) & (s + Up)` which can result
in out-of-bounds errors for the SquareBB[] array if s in the
last rank of the board.

We coorect the bug, and also add some asserts in bitboard.h to
make the code more robust for this particular bug in the future.

Bug report by Joost VandeVondele. Thanks!

Bench: 5512000
This commit is contained in:
Stéphane Nicolet 2018-05-02 13:20:47 +02:00 • committed by Stéphane Nicolet
parent 12ef8f71a2
commit 06e0134cbc
2 changed files with 8 additions and 3 deletions
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5
src/bitboard.h
View file

@ -107,22 +107,27 @@ extern Magic BishopMagics[SQUARE_NB];
/// whether a given bit is set in a bitboard, and for setting and clearing bits.
inline Bitboard operator&(Bitboard b, Square s) {
assert(s >= SQ_A1 && s <= SQ_H8);
return b & SquareBB[s];
}
inline Bitboard operator|(Bitboard b, Square s) {
assert(s >= SQ_A1 && s <= SQ_H8);
return b | SquareBB[s];
}
inline Bitboard operator^(Bitboard b, Square s) {
assert(s >= SQ_A1 && s <= SQ_H8);
return b ^ SquareBB[s];
}
inline Bitboard& operator|=(Bitboard& b, Square s) {
assert(s >= SQ_A1 && s <= SQ_H8);
return b |= SquareBB[s];
}
inline Bitboard& operator^=(Bitboard& b, Square s) {
assert(s >= SQ_A1 && s <= SQ_H8);
return b ^= SquareBB[s];
}

6
src/pawns.cpp
View file

@ -226,8 +226,8 @@ Value Entry::evaluate_shelter(const Position& pos, Square ksq) {
enum { Unopposed, BlockedByPawn, Unblocked };
constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
constexpr Bitboard BlockRanks = (Us == WHITE ? Rank2BB | Rank3BB : Rank7BB | Rank6BB);
constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
constexpr Bitboard BlockRanks = (Us == WHITE ? Rank1BB | Rank2BB : Rank8BB | Rank7BB);
Bitboard b = pos.pieces(PAWN) & (forward_ranks_bb(Us, ksq) | rank_bb(ksq));
Bitboard ourPawns = b & pos.pieces(Us);
@ -235,7 +235,7 @@ Value Entry::evaluate_shelter(const Position& pos, Square ksq) {
Value safety = (ourPawns & file_bb(ksq)) ? Value(5) : Value(-5);
if ((theirPawns & (FileABB | FileHBB) & BlockRanks) & (ksq + Up))
if ((shift<Down>(theirPawns) & (FileABB | FileHBB) & BlockRanks) & ksq)
safety += 374;
File center = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));