Remove candidate passers w/o feasible lever

[Lolligerhans]

Objections from anyone to code style would best be raised now. Specifically regarding

1. the way I nest operations in lengthy instructions and
2. the use of const to help readers and compiler to better understand the computations.

Commit message will not show the fancy ASCII if viewed without monospace font. I like including the pictures though - nobody should be bothered reading text or even diff. The text will remain readable. Wrapped at 50/72.

Testing on takes 4 and 5 is ongoing but not promising.

I add a comment in pawns.cpp to remind readers that identification of candidate passers continues in evaluate.cpp.

I use the phrasing "candidate passer" with a meaning distinct from the one used in recent "Retire candidate passed pawns" commit, which abandoned spacial handling of a different form of "candidate passer".

You do not need to edit this commit. Comment here - I will edit the branch as required.

[Lolligerhans]

Updated bench.

[vondele]

nice idea... for the formatting, try to blend in the code as much as possible, i.e. use same indentation style (which tends to align near = signs). That's a little more difficult with the const decl, which presumably for variables with such a local scope doesn't bring much neither for the compiler nor for the reader.

[Alayan-stk-2]

Excellent commit message.

[snicolet]

@Lolligerhans

Nice idea ! Concerning the formatting, I suggest something like the following version where I used only two bitboards, declaring them at the top of the function as usual -- didn't verified that the bench is the same, however, please double-check -- and put a singular in the comment:

Bitboard b, bb, squaresToQueen, unsafeSquares, candidatePassers, leverable;

...

candidatePassers = b & shift<Down>(pos.pieces(Them, PAWN));

if (candidatePassers)
{
    // Can we lever the blocker of a candidate passer?
    leverable =   shift<Up>(pos.pieces(Us, PAWN))
               &  ~pos.pieces(Them)
               & (~attackedBy2[Them] | attackedBy[Us][ALL_PIECES])
               & (~(attackedBy[Them][KNIGHT] | attackedBy[Them][BISHOP])
                 | (attackedBy[Us  ][KNIGHT] | attackedBy[Us  ][BISHOP]));

    // Remove candidate otherwise
    b &= ~(candidatePassers & ~(shift<WEST>(leverable) | shift<EAST>(leverable));
}

[Lolligerhans]

• Align at equal sign as suggested by vdv and sn.
• Squeezed removal &= into 1 expression. Decided to de morgan it (line exceeded 80c).
• Fixed typo in comment using plural.
• Removed all const and moved declarations to start.
• Double-checked: executable remains identical.

[vondele]

LGTM, will merge in the next round.

The commit message has one more typo (s/althogh/although/g) and maybe you can use the same format (including link location) for the SPRT results as most other commit messages.

[Lolligerhans]

• Fixed altho(u)gh and some bracing in commit message text.
• Adjusted test report formatting. Found multiple variants, including ones omitting links. Copied what seems the most reasonable.

[adentong]

Really nice commit message! Good stuff.

[vondele]

Thanks!