Author: Tony Werten
Date: 01:31:48 04/19/00
Go up one level in this thread
On April 19, 2000 at 03:27:16, Dan Newman wrote:
>On April 18, 2000 at 22:44:25, Flemming Rodler wrote:
>
>>Hi,
>>
>>I am trying to implement a bitboard based chess program on a Pentium or AMD
>>computer. I need to be able to find the following information fast:
>>
>>1) The position of the first and/or last bit in a sequence of 64 bits.
>>2) Count the number of bits that are 1 in a sequence of 64 bits.
>>
>>I know there is a method that works linear in the number of on-bits for
>>problem 2:
>>
>> for(count = 0; bitboard; count++, bitboard &= (bitboard -1));
>>
>>
>>Is there anything faster, ie. such lookuptables or machine code intrutions?
>>
>>What about problem 1?
>>
>>Thanks in advance for any reply
>>Flemming
>
>
>The following is what I use in my program to find bit indices
>(it works only with MSVC).
>
>#pragma warning( push)
>#pragma warning( disable: 4035)
>inline int bsf( unsigned long bitpat)
>{
> __asm mov eax, bitpat
Just a small question. Can you leave this mov away ? Since bitpat will be passed
in the eax register anyway ? Or doesn't this work for inline functions ?
( I'm a delphi man, and delphi doesn't support inline )
Tony
> __asm bsf eax, eax
>}
>inline int bsr( unsigned long bitpat)
>{
> __asm mov eax, bitpat
> __asm bsr eax, eax
>}
>#pragma warning( pop)
>
>
>-Dan.
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