Difference between revisions of "Fill by Subtraction"

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Revision as of 20:13, 10 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);
}

See also

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