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Resource for bit twiddlers
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Gerd Isenberg



Joined: 08 Mar 2006
Posts: 1802
Location: Hattingen, Germany
PostPost subject: Re: Resource for bit twiddlers    Posted: Fri Jun 01, 2007 8:19 am Reply to topic Reply with quote
Pradu wrote:
Gerd Isenberg wrote:


Hi Pradu,

no, the o^(o-2r) trick with r is subset of o, unfortunately works only for "positive" directions, in this setwise case for the a->h direction (east, right from white points of view on the chessboard) with mapping a1==0, h8==63. For all other seven directions one has to use Steffan Westcott's Kogge-Stone routines.
My mistake. I guess also that my code doesn't work well sometimes for multiple rooks on the same rank when one rook coincides with an occupancy. I need to look at your code a bit more closely.

Code:

               hex    bin        bin
            arithmetical order   reversed according to the a1 = 0 mapping
o              0xDB   11011011   11011011   occupancy including rooks
r = subset(o)  0x12   00010010   01001000   rooks
o - r          0xC9   11001001   10010011   occupancy excluding rooks
o - 2r         0xB7   10110111   11101101   subtracting rooks from either next higher occupancy or borrow
o ^ (o - 2r)   0x6C   01101100   00110110   rook attacks of both rooks

You can not do it the other way around - subtracting none-rooks from rooks to get the opposite direction Wink
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Display posts from previous:   
Subject Author Date/Time
Resource for bit twiddlers J. Wesley Cleveland Fri May 04, 2007 1:55 am
      Re: Resource for bit twiddlers Gerd Isenberg Mon May 28, 2007 12:40 pm
            Re: Resource for bit twiddlers Gerd Isenberg Mon May 28, 2007 3:16 pm
                  Re: Resource for bit twiddlers Gerd Isenberg Mon May 28, 2007 4:35 pm
                        Re: Resource for bit twiddlers Gerd Isenberg Wed May 30, 2007 5:55 pm
                              Re: Resource for bit twiddlers Pradu Kannan Wed May 30, 2007 10:51 pm
                                    Re: Resource for bit twiddlers Gerd Isenberg Thu May 31, 2007 6:17 am
                                          Re: Resource for bit twiddlers Pradu Kannan Fri Jun 01, 2007 12:16 am
                                                Re: Resource for bit twiddlers Gerd Isenberg Fri Jun 01, 2007 8:19 am
            Re: Resource for bit twiddlers Gerd Isenberg Mon Jun 04, 2007 2:58 pm
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