Author: Dan Newman
Date: 11:13:05 04/19/00
Go up one level in this thread
On April 19, 2000 at 04:31:48, Tony Werten wrote:
>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
>
Well, I haven't tried that. I think that MSVC's default argument passing
scheme is by stack rather than register. I'll have to try it (with passing
via registers turned on, I guess)... (It could be, since this is inline,
that the optimizer gets rid of any extra move anyway and just arranges for
a copy of the argument to end up in eax just before the BSF.)
-Dan.
>> __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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