Re: [Freeciv-Dev] grid lines

[Trent Piepho <xyzzy@xxxxxxxxxxxxxxxx>]

On Thu, 18 Mar 1999, Vasco Alexandre Da Silva Costa wrote:
> Why are you doing that x*NORMAL_TILE_WIDTH stuff over and over again?
> Most things can be precalculated...
> 
>     n_tile_x *= NORMAL_TILE_WIDTH;
>     n_width *= NORMAL_TILE_WIDTH;
> 
>     n_tile_y *= NORMAL_TILE_HEIGHT;
>     n_height *= NORMAL_TILE_HEIGHT;
> 
>     for(x=tile_x; x<=n_tile_x+n_width; x+=NORMAL_TILE_WIDTH)
>       XDrawLine(display, map_canvas_store, civ_gc, 
>                 x, n_tile_y,
>               x, n_tile_y+n_height);
> 
>     for(y=tile_y; y<=n_tile_y+n_height; y+=NORMAL_TILE_HEIGHT)
>       XDrawLine(display, map_canvas_store, civ_gc, 
>                 n_tile_x, y,
>               n_tile_x+n_width, y);

Why do n_tile_x+n_width over and over again?  That's another loop invariant
that can be moved out.

    y1 = tile_y*NORMAL_TILE_HEIGHT; y2 = (tile_y+height)*NORMAL_TILE_HEIGHT;
    x1 = tile_x*NORMAL_TILE_WIDTH; x2 = (tile_x+width)*NORMAL_TILE_WIDTH;
    for(x=x1; x<=x2; x+=NORMAL_TILE_WIDTH)
      XDrawLine(display, map_canvas_store, civ_gc, x, y1, x, y2);
    for(y=y1; y<=y2; y+=NORMAL_TILE_HEIGHT)
      XDrawLine(display, map_canvas_store, civ_gc, x1, y, x2, y);

I thought gcc would be smart enought to notice the loop invariants, but it
seems it isn't.  It doesn't make a lot of difference though.  I tried timing
both versions with the pentium cycle counter, and there's really no detectable
difference.