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Subject: Re: Fast hash key method - Revisited!

Author: Ernst A. Heinz

Date: 10:53:59 01/14/98

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On January 14, 1998 at 13:20:48, John Scalo wrote:
>
>Say you have nothing but two kings on the board; white king at c2 and
>black king at c7. Now take these two series of moves:
>
>Seq A:                 Seq B:
>c2-c3  c7-c6           c2-c1  c7-c6
>c3-b2                  c1-b2
>
>In both sequences, you end up with the same position: wk on b2, bk on
>c6.
>
>The key in seq A would be something like:
>origKey ^ randTable[white][king][c3] ^
>          randTable[black][king][c6] ^
>          randTable[white][king][b2]

No, you forgot to "clear" the king from each of its source squares
when moving. The "clear operation" is just another XOR such that you
get the following:

seq A = origKey ^ randTable[white][king][c2]    /* "clear" */
                ^ randTable[white][king][c3]    /* "set" */

                ...
=Ernst=



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