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Do not assume that enum are signed

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Clang 3.5 issues warning on constructs like: abs(f1 - f2). The thing is that
f1 and f2 are enum types, and the range given (all positive) allows the
compiler to choose an unsigned type (efficiency being one reason to prefer
unsigned arithmetic). If f1 < f2 are unsigned, then f1 - f2 wraps around zero
and the abs() becomes a no-op. It's the reinterpretation of the unsigned
result (large value) as a signed int that happens to give the correct result,
thanks to 2's complement. This is all tricky and dangerous!

In the spirit of the standard, we assume nothing on the signedness of enums,
and simply calculate the rank and file distances as:
- rank_dist(r1, r2) = r1 < r2 ? r2 - r1 : r1 - r2
- file_dist(f1, f2) = f1 < f2 ? f2 - f1 : f1 - f2
this logic can in fact be applied to any enum we may use, so for better
generality and to avoid code duplication, we use a template function diff()
here.

No functional change.

Resolves #95
This commit is contained in:
lucasart
2014-11-04 00:35:02 +08:00
committed by Gary Linscott
parent 8ab9c2511a
commit d12378497c
3 changed files with 6 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
src/endgame.cpp
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@@ -479,7 +479,7 @@ ScaleFactor Endgame<KRPKR>::operator()(const Position& pos) const {
if ( r == RANK_6
&& square_distance(bksq, queeningSq) <= 1
&& rank_of(wksq) + tempo <= RANK_6
&& (rank_of(brsq) == RANK_1 || (!tempo && abs(file_of(brsq) - f) >= 3)))
&& (rank_of(brsq) == RANK_1 || (!tempo && dist(file_of(brsq), f) >= 3)))
return SCALE_FACTOR_DRAW;
if ( r >= RANK_6
@@ -535,7 +535,7 @@ ScaleFactor Endgame<KRPKR>::operator()(const Position& pos) const {
{
if (file_of(bksq) == file_of(wpsq))
return ScaleFactor(10);
if ( abs(file_of(bksq) - file_of(wpsq)) == 1
if ( dist(file_of(bksq), file_of(wpsq)) == 1
&& square_distance(wksq, bksq) > 2)
return ScaleFactor(24 - 2 * square_distance(wksq, bksq));
}
@@ -749,7 +749,7 @@ ScaleFactor Endgame<KBPPKB>::operator()(const Position& pos) const {
&& opposite_colors(ksq, wbsq)
&& ( bbsq == blockSq2
|| (pos.attacks_from<BISHOP>(blockSq2) & pos.pieces(weakSide, BISHOP))
|| abs(r1 - r2) >= 2))
|| dist(r1, r2) >= 2))
return SCALE_FACTOR_DRAW;
else if ( ksq == blockSq2