Author: Christophe Theron
Date: 18:02:15 06/20/00
Go up one level in this thread
On June 20, 2000 at 14:51:25, Tom Kerrigan wrote:
>On June 20, 2000 at 14:21:23, Christophe Theron wrote:
>
>>On June 20, 2000 at 11:17:48, Andrew Williams wrote:
>>
>>>On June 20, 2000 at 09:02:26, Robert Hyatt wrote:
>>>
>>>>On June 20, 2000 at 04:55:22, Dann Corbit wrote:
>>>>
>>>>>On June 20, 2000 at 04:41:47, James Robertson wrote:
>>>>>
>>>>>>Ignore all results from my previous post "Rough comparison between ro....". I
>>>>>>made some stupid coding errors in my test rotated bitboard code. Once fixed the
>>>>>>rotated bitboards look very competitive against 0x88. :) I also found flaws in
>>>>>>my 0x88 code, but they were very minor and I think I caught all of them (correct
>>>>>>move lists are generated in all my test positions).
>>>>>>
>>>>>>I am very happy to continue to use rotated bitboards. Thanks Robert for
>>>>>>inventing them, and thanks Tim for showing me how to use them!
>>>>>
>>>>>What was the timing ratio for various operations between the two methods?
>>>>>
>>>>>For the 0x88, what board size did you use?
>>>>
>>>>
>>>>For 0x88 you don't have much choice... it has to be 128, where you use the left
>>>>half for the board, the right half (64 squares) are off the board. There is
>>>>really a top half of 128 words also, but 0x88 eliminates references to them
>>>>due to the 0x80 bit not being allowed.
>>>
>>>Christophe Theron posted a few interesting pointers to using 16x16 instead of
>>>16x8 last week (I think).
>>>
>>>Andrew
>>
>>
>>Yes. I think that comparing 0x88 and bitboards is not totally relevant, as 0x88
>>is in my opinion suboptimal. I explained why in last week's posts.
>>
>>There are also many smart tricks you can use that are derived from the
>>properties of a 16x16 (or 16x12) board, and they have never been published.
>>
>>I don't believe it is possible to compare 0x88, 16x and bitboards in one day or
>>two. Once you start to use one system, you discover smart ways to optimize it
>>even months after you start using it.
>>
>>I think that 16x and bitboards just break even, even on 64 processors, but it
>>would probably be very difficult to demonstrate this...
>
>But with bitboards, there is more memory overhead. Sometimes you have to take
>that into consideration. With modern desktop PC processors, it's probably not a
>big deal. But I'd like my program to run on smaller computers (specifically
>palmtops) so I'm going with 0x88.
>
>-Tom
That's a good reason indeed, and could even be the ultimate argument to say that
bitboards are not the best way to go.
Some people are not afraid to allocate a bunch of 64 bits (=8 bytes) integers. I
am. I don't want to blow out the cache of my processor.
Some will say that in a few years from now L1 caches will be much bigger.
I'm not sure. I'm not even sure that 64 bits processors will be so common.
I think the actual trend of microprocessors, from now on, will be: 32 bits
processors consuming less power.
Too PC-centric people will not understand what I mean.
Christophe
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