[Freeciv-Dev] Re: somebody fix struct *player! (was: FoW remove player bug)

[Thue Janus Kristensen <thue@xxxxxxx>]

On Wed, 17 May 2000, Jules Bean wrote:
> On Wed, May 17, 2000 at 03:36:11PM +0200, Thue Janus Kristensen wrote:
> > Just a note: I am going to apply a patch that makes some functions that
> > access bitvectors in maphand.c use playerid instead of struct player
> > *pplayer.
> > 
> > This should be done as it is a waste of CPU to extract the player number
> > (index in the bitvectors) from player struct each time the functions are
> > called. (and it is called a lot)
> 
> This is probably a great idea for clean code, but I'd just like to
> point out that the CPU argument is bogus ;-) The time to dereference a
> pointer is a single cycle, (assuming it's in a cache) and that's just
> not going to stack up compared to the path-finding code which we all
> suspect is the current bottleneck.
> 
> Optimisations like this are good for programmer efficiency and code
> simplicity, but it's not where we're going to find performance
> increases...

But if dereferncing means that it has to load the player struct into
cache it makes a bigger difference.
The pathfinding takes a long time because it checks a large number of
tiles. In each of these checks a part is accesing these bitvectors, so I
would think it could make a difference.

Btw; maybe these oneilne functions like map_get_know() should be made into
macros to avoid the overhead of a function call; is the saving worth it?
Is there any reason not to?

-Thue