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Introduce single_bit() helper

Browse source 
Self-documenting code instead of a tricky
bitwise tweak, not known by everybody.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2012-03-04 23:26:08 +01:00
parent cf0561d31a
commit 19540c9ee8
4 changed files with 11 additions and 4 deletions
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8
src/bitboard.h
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@ -207,6 +207,14 @@ inline Bitboard same_color_squares(Square s) {
} }
/// single_bit() returns true if in the 'b' bitboard is set a single bit (or if
/// b == 0).
inline bool single_bit(Bitboard b) {
return !(b & (b - 1));
}
/// first_1() finds the least significant nonzero bit in a nonzero bitboard. /// first_1() finds the least significant nonzero bit in a nonzero bitboard.
/// pop_1st_bit() finds and clears the least significant nonzero bit in a /// pop_1st_bit() finds and clears the least significant nonzero bit in a
/// nonzero bitboard. /// nonzero bitboard.

2
src/evaluate.cpp
View file

@ -517,7 +517,7 @@ namespace {
assert(b); assert(b);
if (!(b & (b - 1)) && (b & pos.pieces(Them))) if (single_bit(b) && (b & pos.pieces(Them)))
score += ThreatBonus[Piece][type_of(pos.piece_on(first_1(b)))] / 2; score += ThreatBonus[Piece][type_of(pos.piece_on(first_1(b)))] / 2;
} }

3
src/position.cpp
View file

@ -379,8 +379,7 @@ Bitboard Position::hidden_checkers() const {
{ {
b = squares_between(ksq, pop_1st_bit(&pinners)) & occupied_squares(); b = squares_between(ksq, pop_1st_bit(&pinners)) & occupied_squares();
// Only one bit set and is an our piece? if (b && single_bit(b) && (b & pieces(sideToMove)))
if (b && !(b & (b - 1)) && (b & pieces(sideToMove)))
result |= b; result |= b;
} }
return result; return result;

2
src/search.cpp
View file

@ -1351,7 +1351,7 @@ split_point_start: // At split points actual search starts from here
// Rule 1. Checks which give opponent's king at most one escape square are dangerous // Rule 1. Checks which give opponent's king at most one escape square are dangerous
b = kingAtt & ~pos.pieces(them) & ~newAtt & ~(1ULL << to); b = kingAtt & ~pos.pieces(them) & ~newAtt & ~(1ULL << to);
if (!(b && (b & (b - 1)))) if (single_bit(b)) // Catches also !b
return true; return true;
// Rule 2. Queen contact check is very dangerous // Rule 2. Queen contact check is very dangerous