Author: Reinhard Scharnagl
Date: 23:57:37 02/27/06
Go up one level in this thread
On February 27, 2006 at 15:56:14, Steffan Westcott wrote:
>On February 27, 2006 at 13:36:52, Gerd Isenberg wrote:
>
>>Hi,
>>
>>while i indulge my current morbus knuth attack, which hits me so one, two times
>>a year, i like to ask a question related to the "rotated" De Bruijn generator.
>>
>>I have a word "d" with a setwise interpretation ( a bitboard) and maximum
>>cardinality of N (N bits set, let say 8). I like to enumerate all subsets,
>>including the empty set and the original complete set. Looking for a smarter
>>algorithm.
>>
>
>Perhaps I missed something, but isn't this just a case of incrementing a number
>and rippling a carry through the unwanted bits? Here is my answer, anyhow:
>
>void enumsets(const BitBoard d)
>{
> BitBoard n = 0;
> do {
> do_something_with_set(n);
> n = (n-d) & d;
> } while (n);
>}
>
>
>Cheers,
>Steffan
When I had been working with a 0x88 structure I used to iterate by:
coor = ((coor | ~0x77) + 1) & 0x77;
thus handling the coordinate bit combinations of 0x77;
But your method above is indeed simpler and faster.
Reinhard.
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