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Chess op code

A CPU instruction which makes a chess move
  [vote for,

I note that there is such a thing as an op code in x86 CPUs which returns the approximate value of pi. If this is calculated using some kind of algorithm rather than, as I suspect, just hanging out stored somewhere on the CPU itself, it would be a nice achievement. GPUs are clearly capable of doing clever stuff quickly too.

In 1982, a ZX81 program was published which played chess in 672 bytes or thereabouts of Z80 machine code. This is not vastly beyond, and may even be less complex than, calculating pi to a certain number of places or doing 3-D graphics.

It ought to be possible to furnish a CPU with the ability to play chess by putting a particular op code in its instruction set. This could operate in one of two ways. It could either interpret the next four bytes as algebraic notation for a chess move and plonk a four byte value in a register, memory location or on a stack which represented its response similarly, or it could use a sixty-four nibble area of memory representing a chess board and modify it accordingly.

This would be cheating of course, but it would also break all records, probably permanently, for short chess programs, as it would be chess in one byte, excluding operands. Fanciness could ensue as usual in the form of pretty raytraced boards or whatever, but the core of the program would be just that single byte.

I presume 1K chess was very poor, but it could still be used as the basis of possible moves which could then be improved. Moreover, doing this might furnish the CPU with other facilities in the meantime which would enable it to do other things very efficiently such as play draughts relatively simply. It would also be humongously fast.

I want it implemented in hardware rather than microcode, and the rest of the instruction set could be RISC if you like to compensate.

nineteenthly, Jan 18 2017

Wikipedia: PGN https://en.wikipedi...table_Game_Notation
Portable Game Notation, used by lots of chess programs as an input/output/serialisation format. [zen_tom, Jan 18 2017]

Wikipedia: Shannon Number https://en.wikipedi...wiki/Shannon_number
An estimate of the size of the permutation space for chess. [zen_tom, Jan 18 2017]

Wikipedia: Chess Board Representation https://en.wikipedi...resentation_(chess)
[zen_tom, Jan 18 2017]


       There ought to be some standard mapping of the permutations of positions of pieces on a chessboard to a value - if this can be identified, or codefied in some way, it might act as a convenient input output device, i.e. feed in the number representing the current board-state, and the operation would return a value corresponding to the state after the move. This number is likely to be rather large, and probably wouldn't fit into 4 bytes (slight understatement - see Shannon Number - link).   

       Sorry, talking out of my hat here! I was starting to think, "How does *anyone* represent a chessgame?" and there are of course lots of simpler arrangements e.g. FEN.   

       An alternative would be to use PGN, but that's pretty verbose, and could end up being rather large too.
zen_tom, Jan 18 2017

       The thing is, there's no need for a computer to be able to make a poor chess move at lightning speed. Either it's playing against a human, in which case it has millions of full cycles before the human can even recognize what move was made, or it's playing against another machine, in which case moves from the 1000 byte program won't teach us anything no matter how many there are.
Voice, Jan 18 2017

       Once you can operate with the number of atoms in the universe (or the neighborhood thereof), chess is just tic-tac- toe
theircompetitor, Jan 18 2017

       It shouildn't surprise me that there's an internal notation, but thanks for that. The reason I thought in terms of nybbles is that to my mind there seem to be thirteen possibilities: one of six possible pieces of each colour or an empty square. If there's a standard, compact way of doing that, fine - rather like the IEEE representation of floating point numbers, if that's what it is.   

       You could indeed argue that there's no need for this, which to me is not the same as not wanting to do it because the idea is "there". Having said that, I can see positive fallout from it. The hardware which made this possible would make other things possible too if portions of it were available for those other uses, and it's even conceivable that the whole architecture could be optimised for chess. For instance, maybe the data bus could be 256 bits which could be used as a chessboard, accessible in eight 32-bit words, each representing a row.
nineteenthly, Jan 18 2017

       If a design decision is useful for other purposes there's no need to discuss chess to decide whether to implement it. If you just want to propose arbitrary solutions that may come in handy other ways any arbitrary solution will do. The processor best suited to running a sewing machine, or op codes for finding rhyming words.
Voice, Jan 18 2017

       I've implemented chess engines multiple times, including on mobile phones in those days when efficiency still mattered on mobile phones.   

       Ultimately the strength of a typical chess program (i.e. not one designed to beat the world champion, but more so for a subway ride) is in the size of the opening book, and therefore the density of describing positions (so as to store a larger opening book) is of some meaningful value.
theircompetitor, Jan 18 2017

       [Voice], computers are to my mind general purpose machines with unanticipated applications. As they are now, they seem to be primarily devices which do Boolean algebra which has been extended to arithmetic. This has taken them in unexpected directions and it's easier to get them to do some things than others. The things it's easier to do with a chess-oriented computer might turn out to be things which are harder for an arithmetic- oriented one to do, or of course there might be some mathematical proof that that's not so. It might also be harder to do other things, but then this is a generalised computer as well as a chess one.   

       [theircompetitor], would it help at all if there was a bad chess algorithm churning out some poor moves very quickly which could then be assessed by a better one?   

       I also now really, really want to know how the ZX81 program worked. I've been assuming up until now that it was just a computer representation of a chessboard which two players could use, but obviously I was wrong.
nineteenthly, Jan 18 2017

       [nineteenthly] sure, in the "Shall We Play A Game" mode (i.e. testing all possibilities, where all is larger than the # of atoms in the universe, at least until we figure out the dark matter thingy)
theircompetitor, Jan 18 2017

       I think you would need more than a single instruction, at the very least you would need another to reset the board.   

       Many CPUs have opcodes that correspond directly to dedicated hardware, for instance a shift operation might invoke a barrel shifter, a dedicated circuit just for doing multiple shifts. Also, some CPUs take many cycles to complete single instructions.   

       So, just grab an existing chess computer, and plug it into your CPU as a dedicated hardware chess circuit.
mitxela, Jan 18 2017

       That's allegedly similar to the way they used to add an arithmetic co- processor to CP/M machines by sticking a calculator chip in there. It seems quite inelegant and it'd be pretty slow.   

       If it was done via a data structure representing the board, only one instruction would be needed. The board could be initialized on reset and future games could be set up through procedures. However, abandoning a game would be messy.
nineteenthly, Jan 19 2017


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