Author: Bas Hamstra
Date: 18:20:57 02/10/04
Go up one level in this thread
On February 10, 2004 at 11:28:48, Vincent Diepeveen wrote:
>On February 10, 2004 at 10:57:15, Bas Hamstra wrote:
>
>>On February 09, 2004 at 09:07:41, Gerd Isenberg wrote:
>>
>>>On February 09, 2004 at 05:09:07, Renze Steenhuisen wrote:
>>>
>>>>
>>>>Hi there!
>>>>
>>>>does anyone know the fastest way to determine the lcoation of the Least/Most
>>>>Significant Bit, and to clear that bit?
>>>>
>>>>In my case the most important platforms (at the moment) are Pentium III and IV.
>>>>
>>>>Thanks!
>>>
>>>find lsb from CCC archives:
>>>
>>>http://chessprogramming.org/cccsearch/ccc.php?art_id=265616
>>>
>>>Walter Faxon's magic BitScan:
>>>http://chessprogramming.org/cccsearch/ccc.php?art_id=272378
>>>
>>>Matt Taylor's De Bruijn folding trick:
>>>http://chessprogramming.org/cccsearch/ccc.php?art_id=305965
>>>
>>>Gerd
>>>
>>>
>>>>
>>>>Renze
>>
>>Gerd,
>>
>>IMO the BSF instruction is still fastest. Don't test this in loops, in a
>>searching engine you get quite different results and BSF is in my case clearly
>>the winner, especially for the paltforms he mentiones, and besides he is not
>>talking 64 bit...
>>
>>
>>Bas.
>
>It depends upon which CPU you use Bas.
>
>In diep i'm using a simple table lookup for several years already; later i found
>out that Nalimov had posted similar code here for 64 bits bitboards.
>
>But well i'm not 64 bits bitboards so in 32 bits it's a lot easier :)
>
>The reasons why i'm not using BSF has however a different cause than the reason
>why Nalimov posted it without BSF here. I simply want to avoid inline assembly
>wherever possible.
>
>For me that is a convincing argument favouring Eugene's code :)
>
>>
>>int LastOne(unsigned int Number)
>>
>>{ asm mov EAX, Number
>> asm BSF EAX, EAX
>>}
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