Author: Ed Schröder
Date: 22:06:43 06/21/00
Go up one level in this thread
On June 21, 2000 at 21:51:01, Robert Hyatt wrote:
>On June 21, 2000 at 19:14:24, Tom Kerrigan wrote:
>
>>On June 21, 2000 at 17:16:05, Robert Hyatt wrote:
>>
>>>On June 21, 2000 at 14:52:34, Tom Kerrigan wrote:
>>>
>>>>On June 21, 2000 at 14:38:23, Christophe Theron wrote:
>>>>
>>>>>On June 21, 2000 at 13:33:14, Tom Kerrigan wrote:
>>>>>
>>>>>>On June 20, 2000 at 21:39:01, Robert Hyatt wrote:
>>>>>>
>>>>>>>On June 20, 2000 at 15:52:53, Tom Kerrigan wrote:
>>>>>>>
>>>>>>>>On June 20, 2000 at 15:03:48, Robert Hyatt wrote:
>>>>>>>>
>>>>>>>>>On June 20, 2000 at 14:07:39, Tom Kerrigan wrote:
>>>>>>>>>
>>>>>>>>>>On June 19, 2000 at 21:32:56, Robert Hyatt wrote:
>>>>>>>>>>
>>>>>>>>>>>On June 19, 2000 at 20:50:11, John Coffey wrote:
>>>>>>>>>>>
>>>>>>>>>>>>On June 19, 2000 at 19:48:36, Larry Griffiths wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>>I have found bitboards to be an even trade-off on my Pentium system. I have to
>>>>>>>>>>>>>update about 6 bitboards when a piece moves and this generates a lot of
>>>>>>>>>>>>>instructions. I get it back in my IsKingInCheck code so it evens out. I like
>>>>>>>>>>>>>to have fast move generation code, but most of my gains have been through
>>>>>>>>>>>>>alpha-beta, hash-table, killer-move and movelist ordering etc.
>>>>>>>>>>>>>
>>>>>>>>>>>>>Larry.
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>>Maybe I am too much of a novice, but I don't see yet why I should convert over
>>>>>>>>>>>>to bitboards. Is move generation faster? If so, why? My program scans the
>>>>>>>>>>>>board and uses simple loops to generate moves. Do you not have to do loops
>>>>>>>>>>>>with bitboards?
>>>>>>>>>>>
>>>>>>>>>>>Not to generate moves, No. You generate all the sliding piece moves with two
>>>>>>>>>>>table lookups...
>>>>>>>>>>
>>>>>>>>>>Hmmm. I do table lookups all over my program, and none of them seem to be
>>>>>>>>>>generating any moves...
>>>>>>>>>>The fact is that you DO need to loop to generate moves in a bitboard program.
>>>>>>>>>>Maybe it's not the same loop, but it's still a loop.
>>>>>>>>>>
>>>>>>>>>>-Tom
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>Who says so? Ask the Dark Thought guys.
>>>>>>>>>Or Slate/Atkin. You only need to loop if you want to take the attack bitmap
>>>>>>>>>and turn it into a list of moves. This is not the way _all_ programs operate
>>>>>>>>>(chess 4.x, Dark Thought, others, any of which generate a few moves at a time,
>>>>>>>>>then take one and search it, without enumerating the other moves.)
>>>>>>>>>
>>>>>>>>>So loops are something you do (with bitmaps) if you want to, not because you
>>>>>>>>>have to.
>>>>>>>>>
>>>>>>>>>As far as your table lookups not generating any moves, that is a programming
>>>>>>>>>issue. Mine do. :)
>>>>>>>>
>>>>>>>>Maybe your makemove() function can take bitboards as input (i.e., here is a set
>>>>>>>>of squares that my pieces can move to) but mine sure can't.
>>>>>>>>-Tom
>>>>>>>
>>>>>>>
>>>>>>>You are missing the point. A move generator _can_ emit a single move, which
>>>>>>>can be fed into MakeMove(). Read "Chess Skill in Man and Machine", the chess
>>>>>>>4.x section. They explain this pretty well. It takes zero loops to emit a
>>>>>>>single chess move. You pick the source square. You do two table lookups for
>>>>>>>bishops (say) and you have all the target squares it can move to. A single
>>>>>>>FirstOne() and you have a <to> square, which is all you need to make the move,
>>>>>>>and recursively call Search().
>>>>>>
>>>>>>So you end up having to call gen() a mess of times. I don't see how that isn't a
>>>>>>loop.
>>>>>>-Tom
>>>>>
>>>>>
>>>>>As I understand he says that in order to generate one move he doesn't have to
>>>>>loop. That's what James explains in another post.
>>>>>
>>>>>With 0x88 or 16x you have to loop thru empty squares, he says with bitboards you
>>>>>don't have to. For each rank, file or diagonal in any configuration (by
>>>>>configuration I mean set of empty squares in this rank/file/diagonal), you can
>>>>>have precomputed arrays that instantly give you the set of squares (a bitboard)
>>>>>a sliding piece can move to.
>>>>>
>>>>>Not that I support his point of view about bitboards. I prefer to "loop thru
>>>>>empty squares" in my L1 cache rather than clobbering the same cache with
>>>>>bitboards. And anyway, the time required to extract the rank/file/diagonal from
>>>>>the "occupied" bitboard and the time required to process the resulting set of
>>>>>"can move to" squares is not required in 0x88 or 16x. And for non-sliding pieces
>>>>>(which represent in average half of the pieces present on the board), the method
>>>>>does not apply.
>>>>
>>>>Exactly, it's necessary to process the resulting bitboards. Maybe you can do
>>>>some simple operations to get an interesting set of bits, but at some point, you
>>>>have to turn those bits into something useful. There has to be a loop somewhere
>>>>which extracts the bits and does appropriate things to them. If you're lucky,
>>>>your processor has BSF/BSR (or an equivalent) and this loop is relatively fast.
>>>>But if you don't have these instructions, I bet the pretty bit patterns aren't
>>>>helping you much. Personally, I'm a little sick of people saying, "oh, one AND
>>>>operation and I'm done!" and totally ignoring everything else that has to be
>>>>done.
>>>>
>>>>-Tom
>>>
>>>You are not nearly so sick of hearing that as I am sick of hearing people talk
>>>about what you can and can't do with bitboards _without_ ever having tried them.
>>>
>>>Again, there is _no_ need for a loop. I can generate a single move (capture)
>>>with no loop of any kind. Anybody can generate a non-capture (single move)
>>>without a loop, of course. But captures are way more common to want, since
>>>they are usually tried first.
>>
>>Fine, let's review something you said earlier:
>>>Not to generate moves, No. You generate all the sliding piece moves with two
>>>table lookups...
>>
>>So how about you tell me how you're going to generate multiple moves ("all the
>>sliding piece moves") in some sort of machine-usable form without doing a loop?
>>Remember, a loop around the move generator is still a loop. Nobody's asking
>>whether or not you can generate a single stupid capture without a loop, and
>>there's no practical value in that anyway, unless you can be sure that the
>>capture is generated in the correct order.
>
>
>Easy, again from Chess Skill in man and machine. I produce a 64 bit value
>for all the bishop moves, by doing two table lookups. I already know the
><from> square to produce these moves. I use a FirstOne() call to find one
>of the destination squares (<to> square). I clear this bit, save the 64 bit
>vector, and make this move. I recursively call search. When it returns, I
>regrab the 64 bit vector, FirstOne() to find the next destination, make this
>move and again call Search() recursively. The only loop I have is the same
>loop everyone has to select the next move. I have _zero_ loops to _generate_
>the moves.
>
>
>
>>
>>>I've done 0x88, 8X8, 16x16, 10x12, and probably others. I don't think that
>>>move generation is the separating point for bitboards vs the others, except
>>>for the fact that I can generate captures far easier. Bitboards help in other
>>>places as well. And on 64 bit architectures, they make a lot of sense.
>>>
>>>You ought to do what I did 5 years ago. Say "I am going to try this for a
>>>couple of years, to see if this is worthwhile." It takes a lot of time and
>>
>>Remember, I did use bitboards for a while, I know many of the issues involved.
>
>
>I have used them for 5 years. I have learned far more. And I am still finding
>new ways to do things every few months. The learning doesn't stop after using
>them "for a while".
>
>
>
>
>
>>
>>>experience and false starts to do bitboards. But they _can_ work quite well.
>>>I can point to several programs that prove this, from Kaissa and chess 4.x in
>>>the 1970's, thru Crafty and several others in 2000.
>>>
>>>But they _do_ take time to learn, just like a programming language does.
>>
>>You have your way, I have my way. In case you didn't notice, I'm not saying one
>>way is better or worse. (Not in this thread, anyway.) So I don't see why you're
>>being so violently pro-bitboard. All I'm saying is that you should not jump in
>>and say that you can solve the world's problems with a single table lookup,
>>because that's simply not accurate.
>>
>>-Tom
>
>
>I'm not violently pro-bitboard at all. I simply corrected some _wrong_
>information that was being posted here. I've said hundreds of times that
>until we talk about 64 bit cpus, bitboards probably do no better than break
>even with other good approaches. I have also said, hundreds of times, that
>move generation is _not_ the most important thing done in a chess board. At
>least for my code, it is not in the top 5 when you profile things.
>
>As far as a lookup goes, I can generate _all_ sliding piece moves for a bishop,
>with two 64 bit memory loads. I can generate all captures for a bishop just as
>easily, without having to traverse the empty squares. I didn't say any more
>or any less than that. Since in a chess engine, generating captures is a very
>common thing to do, bitboards are good there. They are good in other places.
>They also have their problems. But memory bandwidth is not particularly one of
>them. And on machines like the EV6-based 64 bit architectures, I think bitmaps
>might have a real advantage due to the inherent data density they have.
Having never had the pleasure of dealing with BB's I can understand the
2 x AND to detect the capture. But how do you get the square from the
64 bit integer since you can't address a 64 bit table to get the square
immediately so you have to write a piece of clever code for it, right?
Looks (very) time consuming to me, or?
Ed
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