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Resource for bit twiddlers
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Gerd Isenberg



Joined: 08 Mar 2006
Posts: 1785
Location: Hattingen, Germany
PostPost subject: Re: Resource for bit twiddlers    Posted: Mon May 28, 2007 3:16 pm Reply to topic Reply with quote
Gerd Isenberg wrote:


Code:
u64 eastAttacks(u64 rooks, u64 empty)
{
    const u64 H     = 0x8080808080808080;
    u64 occupied    = rooks | ~empty;
    u64 occNoRook   = rooks ^ occupied;
    u64 difference  = ((occNoRook | H) - (rooks & ~H))
                    ^  (~occupied & H);
    return occupied ^ difference;
}

Gerd


Oups, since

A ^ (~A & B) == A | B

the code becomes a bit cheaper:

Code:
u64 eastAttacks(u64 rooks, u64 empty)
{
    const u64 H     = 0x8080808080808080;
    u64 occInclRook = rooks | ~empty;
    u64 occExclRook = rooks ^ occInclRook;
    u64 attacks     = ((occExclRook | H) - (rooks & ~H))
                    ^  (occInclRook | H);
    return attacks;
}
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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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