Difference between revisions of "Fill by Subtraction"
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'''[[Main Page|Home]] * [[Board Representation]] * [[Bitboards]] * [[Sliding Piece Attacks]] * Fill by Subtraction''' | '''[[Main Page|Home]] * [[Board Representation]] * [[Bitboards]] * [[Sliding Piece Attacks]] * Fill by Subtraction''' | ||
− | Performing the [[Subtracting a Rook from a | + | Performing the [[Subtracting a Rook from a Blocking Piece|o^(o-2r) - trick ]] in a [[SIMD and SWAR Techniques|SWAR-wise]] fashion with bytes (ranks), saves some instructions compared to [[Kogge-Stone Algorithm|Kogge-Stone]]. |
[[include page="MappingHint"]] | [[include page="MappingHint"]] | ||
Unfortunately it only works in positive horizontal direction, so the possible savings are marginal, despite even less generalization of handling one out of eight cases with a different code pattern. | Unfortunately it only works in positive horizontal direction, so the possible savings are marginal, despite even less generalization of handling one out of eight cases with a different code pattern. |
Revision as of 16:42, 18 May 2018
Home * Board Representation * Bitboards * Sliding Piece Attacks * Fill by Subtraction
Performing the o^(o-2r) - trick in a SWAR-wise fashion with bytes (ranks), saves some instructions compared to Kogge-Stone. include page="MappingHint" Unfortunately it only works in positive horizontal direction, so the possible savings are marginal, despite even less generalization of handling one out of eight cases with a different code pattern.
Source Code
U64 eastAttacks(U64 rooks, U64 empty) { const U64 H = 0x8080808080808080; U64 occInclRook = rooks | ~empty | H; U64 occExclRook = (rooks &= ~H) ^ occInclRook; U64 rookAttacks = (occExclRook - rooks) ^ occInclRook; return rookAttacks; }
Even more with vectors of two bitboards and SSE2-instructions.
Comparison with Kogge-Stone
For comparison the Kogge-Stone attack-getter. It gives an idea how to implement a Kogge-Stone Adder with bitwise operations only.
U64 eastAttacks(U64 rooks, U64 empty) { empty &= notAFile; rooks |= empty & (rooks << 1); empty &= (empty << 1); rooks |= empty & (rooks << 2); empty &= (empty << 2); rooks |= empty & (rooks << 4); return notAFile& (rooks << 1); }