[Freeciv-Dev] Re: (PR#7350) Map radius change with city size

["rwetmore@xxxxxxxxxxxx" <rwetmore@xxxxxxxxxxxx>]

<URL: http://rt.freeciv.org/Ticket/Display.html?id=7350 >


This is an attrocious algorithm and the excuses should
be gut wrenching enough to force one to use a little
brain power to fix it ...

Why people think looping over every world possibiity to
do a test in an inner loop for something that can be evaluated
by a little pre-thought to use a *slightly* more efficient
order of evaluation, is some sort of "good" programming
style, and *never* losing a chance to try and slow down
the code, is something I will never understand.

Use brainpower to reorder the loops and document the process.
Leave this behind as a comment if you want to show off poor
programming skills that were avoided or whatever your rationale
for this code is.

Cheers
RossW
=====

Jason Short wrote:
> <URL: http://rt.freeciv.org/Ticket/Display.html?id=7350 >
> 
> I think the generation of the indices is more complicated than it needs
> to be.
> 
> I think this implementation should work:
> 
>   int dist, count = 0;
> 
>   for (dist = 0; dist <= CITY_MAP_RADIUS * CITY_MAP_RADIUS + 2; dist++) {
>     for (x = 0; x < CITY_MAP_SIZE; x++) {
>       for (y = 0; y < CITY_MAP_SIZE; y++) {
>         int dx = (x - CITY_MAP_RADIUS);
>         int dy = (y - CITY_MAP_RADIUS);
> 
>         if (dx * dx + dy * dy == dist) {
>           indices[count].x = x;
>           indices[count].y = y;
>           count++;
>         }
>       }
>     }
>   }
> 
> This is O(R^4), where R = CITY_MAP_RADIUS (or max city radius).  This is
> quite acceptable as a one-time cost.
> 
> jason