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Re: [gnugo-devel] Looping over the board

From: Gunnar Farnebäck
Subject: Re: [gnugo-devel] Looping over the board
Date: Mon, 17 Jan 2005 03:57:41 +0100
User-agent: EMH/1.14.1 SEMI/1.14.3 (Ushinoya) FLIM/1.14.2 (Yagi-Nishiguchi) APEL/10.3 Emacs/21.3 (sparc-sun-solaris2.9) MULE/5.0 (SAKAKI)

Arend wrote:
> An alternative, admittedly uglier solution would be

Well, that construction obviously has to be used as a macro but if
we're going to use a macro anyway it seems better not to have an
indexing matrix that needs to be kept in sync with board_size.

>    #define LOOP_BOARD(pos) \
>      for (pos = BOARDMIN; pos < BOARDMAX; \ 
>         (ON_BOARD(pos++) ? pos : pos = pos + 1 + MAX_BOARD - boardsize))

That was obviously untested code. I assume you meant

#define LOOP_BOARD(pos) \
  for (pos = BOARDMIN; pos < BOARDMAX; \
       pos += ON_BOARD(pos + 1) ? 1 : MAX_BOARD - board_size + 2)


> > The drawback of the last construction is that it's doing a somewhat
> > scary amount of preprocesser magic, hiding a complete for statement in
> > a macro.
> Well, if you suggest it the preprocessor magic cannot be that scary :)

It's a borderline case. I've tested running the loop macro in gdb and
it behaves well, so that is at least not a problem.

> Despite my performance objection I am in favor of your proposal, since
> none of the current board loops are performance critical; we should just
> keep in mind to possibly not use it where loops could become
> bottlenecks.

Yes, we shouldn't really be looping over the board in time critical
code at all.


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