[Freeciv-Dev] Re: Profiling Civserver again

[Lino Mastrodomenico <mastro@xxxxxxxxxx>]

Ross W. Wetmore wrote:
> At 05:21 AM 01/08/01 +0300, Gregory Berkolaiko wrote:
> >Jason is right when he says that cleaning up map_adjust_x should do good.
> >I think a good portion of CPU time spent in get_map_tile is wasted on two
> >modulus ( % ) operations in map_adjust_x.  One is completely unnecessary,
> >as was mentioned earlier.  Is it possible to get rid of the second one(s)
> >in a safe way without converting the macro to a function?
[...]
> If you do the same trick with map_adjust_x, you can test for the border
> cases in one operation and avoid redundant "%"s. If you assume map.xsize
> is always positive (would be an interesting game if it weren't), then you
> can avoid one "%". If you assume the only valid range for out-of-bounds
> is one map.xsize above or below, then you can drop the "%"s. But with the
> added border check, I would not worry about the expense of saving 2 % vs
> adding one "-" on 100 border ops in a 4000 map, since the % is actually
> safer.
>
> #define map_adjust_x(X)                        \
>   ((unsigned)(X) < (unsigned)map.xsize ? (X)   \
>   : ((X) < 0 ? (X) % map.xsize + map.xsize : (X) % map.xsize))

Warning: this change will reopen this bug: 

  http://www.freeciv.org/cgi-bin/bugs?findid=749

And please note that gcc with -O2 is perfectly capable to optimize trivial 
cases like this: the module is performed only once.

E.g.: for the x86 it generates something like this:

***
        movl    map, %ecx
        movl    %edx, %eax
        sarl    $31, %edx
        idivl   %ecx
        testl   %edx, %edx
        jns     .L69
        addl    %ecx, %edx
.L69:
***

ciao

-- 
Lino Mastrodomenico
E-mail: mastro@xxxxxxxxxx