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Subject: additional hint for rotated

Author: Gerd Isenberg

Date: 14:50:07 02/22/06

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>So far so good - similar is possible with rotated. First one may triple the
>rotated lookup-table sizes by introducing not only combined opposite direction
>attacks but also the two disjoint. Second on may also index precalculated
>movelists with occupied state and square index - even if handling captures or
>whether attacked squares ar occupied by own pieces becomes a bit more
>complicated. Keeping direction wise disjoint attacks has some merits - also for
>determing pinned pieces, remove checker x-rays etc.

Also combined opposite ray attacks (e.g. north/south) - as supplied by rotated
lookups - may be easily splitted into two disjoint ray attacks sets, where all
these de Bruijn tricks may be applied.

With d1 == opposite(d2):

 assert((d1Ord2 & sourceBB) == 0);
 d1 = d1Ord2 &  (sourceBB-1);
 d2 = d1Ord2 & ~(sourceBB-1);

Gerd



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