Re: [Gnushogi-devel] gnushogi xboard support

[h . g . muller]

> gnushogi maps the board in a monodimensional array.  While it looks bit
> primitive, and makes move description hard to read by humans, it does have
> some advantages for this promotion-zone issue :)
>
> #define InBlackCamp(sq) ((sq) < 27)
> #define InWhiteCamp(sq) ((sq) > 53)
> #define InPromotionZone(side, sq) \
> (((side) == black) ? InWhiteCamp(sq) : InBlackCamp(sq))

OK, from this it seems that GNU Shogi uses separate code for white and
black moves that you can at compile time decide which test to make by a
macro. In Shokidoki I use the same code for both colors. So it is more
convenient to make a test like (promoGroup[coloredPieceType] &
canPromote[sq]) or (promoGroup[coloredPieceType] & canDefer[sq])  where
pieces of each color just use different bits in promoGroup and zoneFlags.

Monodimensional boards are quite standard in engines for efficiency
reasons; all my engines use them too. There are still different flavors
for how to map the 2d board onto the linear one e.g. whether there are
unused bytes between one rank and the next to act as edge guards and avoid
pieces from wrapping around like the board is a cylinder. And sometimes
also to make that the difference of two square numbers uniquely identifies
the board step.