Rotated Indices

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Rotated indices, a deconcentrated version of rotated bitboards, proposed by Alessandro Damiani as used in his engine Fortress. Instead of using rotated bitboards with packed 15 diagonals and 15 anti-diagonals each, Alessandro applies an array of 16 + 30 rotated indices for all 16 orthogonal and 30 diagonal lines on the board. Those indices are incrementally updated during make/unmake, which takes a tad more effort - but once updated, the rotated indices pay off, the more often they are used inside a node of the search. No further computation is required to look up attacks, pure indexed memory accesses.

The possible disadvantage - rotated indices, similar or slightly worse than rotated bitboards, are not as versatile as techniques relying on one occupancy bitboard only - if it is about a temporary change of the occupancy on the fly for x-rays and pinned pieces etc..

=See also=
 * Flipping Mirroring and Rotating
 * Fortress
 * Rotated Bitboards
 * Rotated Indices in Gk

=Forum Posts=
 * Re: Rotated bitboards by Alessandro Damiani, rgcc, October 31, 1997
 * Re: Resources about rotated bitboards by Alessandro Damiani, CCC, January 16, 2004

=References=

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