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Rewrite backward pawn detection

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Use the new backmost_sq() instead of a loop.

No functional change.
This commit is contained in:
Reuven Peleg 2013-09-03 19:05:53 +03:00 • committed by Marco Costalba
parent 679c2ea227
commit 457ac26de5
1 changed files with 5 additions and 9 deletions
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14
src/pawns.cpp
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@ -140,16 +140,12 @@ namespace {
// We now know that there are no friendly pawns beside or behind this
// pawn on adjacent files. We now check whether the pawn is
// backward by looking in the forward direction on the adjacent
// files, and seeing whether we meet a friendly or an enemy pawn first.
b = pos.attacks_from<PAWN>(s, Us);
// files, and picking the closest pawn there.
b = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
b = pawn_attack_span(Us, s) & rank_bb(backmost_sq(Us, b));
// Note that we are sure to find something because pawn is not passed
// nor isolated, so loop is potentially infinite, but it isn't.
while (!(b & (ourPawns | theirPawns)))
b = shift_bb<Up>(b);
// The friendly pawn needs to be at least two ranks closer than the
// enemy pawn in order to help the potentially backward pawn advance.
// If we have an enemy pawn in the same or next rank, the pawn is
// backward because it cannot advance without being captured.
backward = (b | shift_bb<Up>(b)) & theirPawns;
}