Author: Dann Corbit
Date: 15:29:46 03/03/06
Go up one level in this thread
On March 03, 2006 at 17:14:54, Tony Werten wrote:
>On March 03, 2006 at 15:58:21, Steffan Westcott wrote:
>
>>Gerd,
>>
>>I may have terribly misunderstood things, but there is direct algorithm for
>>mapping the 128 possible attack bitboards to 7 bit numbers. Additionally, the
>>algorithm does not need the location of the ray source square, nor any lookup
>>tables.
>>
>>For a ray along a rank or diagonal, it is sufficient to collapse the files:
>>
>>typedef unsigned __int64 BitBoard;
>>
>>int collapsed_files_index(BitBoard b)
>>{
>> b |= b >> 32;
>> b |= b >> 16;
>> b |= b >> 8;
>> return b & 0xFF;
>>}
>>
>>For a ray along a file, a little more trickery is needed:
>>
>>int collapsed_ranks_index(BitBoard b)
>>{
>> b |= b >> 4; // No masking needed
>> b |= b >> 2; // " "
>> b |= b >> 1; // " "
>> return ((b & 0x0101010101010101) * 0x0102040810204080) >> 56;
>>}
>>
>>Both of the above routines return 8 bit results. Depending on the left/right
>>orientation of the ray in relation to your chosen bitboard bit numbering scheme,
>>you may need to shift the result right by 1 bit.
>>
>>In addition, if you know the co-ordinates of the source square (either at
>>runtime or compile time), simpler variants of the above routines are possible.
>>
>>I don't use techniques like these as I avoid serialisation of moves or features
>>as much as possible. However, I offer you and Dann the above as it may be of
>>interest.
>
>Hi Steffan,
>
>although the algoritm looks simpler (allthough I'm not sure I understand) , (BB
>& mask)*magic_number will give a better performance.
Why not just: switch (BB) {/*128 cases go here */}
?
What is the value of the transform into a shorter integer type?
Has anyone measured that it makes the switch faster? For me it is only
important if it makes it faster for 64 bit hardware anyway.
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.