I just made a wonderful discovery!
The D version is in fact only 7 percent slower than C.
Earlier I mentioned the ONLY difference was the random number generator
- well it turns out the random number generator was a big deal.
The Mersenne twister is apparently far faster than the D library random
number generator I was previously using.
I could not believe the difference, So I wrote a tight loop to generate
random numbers the same number of times the program does and compared
the MT to the library routine. There was about a 5 second difference,
almost the same as the difference in the run-times of the 2 versions.
I still couldn't believe this, so did some sanity checks to make sure
the random numbers were properly distributed. I basically generated a
few million, put them in a file and did sort numbers.txt | uniq -c
which counts how many times each number appeared - I used the randInt
function to get numbers between 0 and 100. I was getting a very nice
distribution - no easily detectable bugs that would cause the anomolies.
Also, I was getting the very same average number of moves per game - a
relatively good indication it's all working properly (and how I found a
previous bug.)
So it appears that D is perfectly usable as a very fast compiled
programming language, at least as compared to gcc with all the
optimizations I know to do.
- Don
On Thu, 2006-12-07 at 12:28 -0500, Don Dailey wrote:
> In fact, I just wrapped this up into my Mersenne twister code - randInt
> is now built in to the library and I eliminated the function call
> overhead of calling rand() (or the mersenne equivalent.) Probably won't
> make a noticeable difference, but since I'm porting it to D anyway, I
> might as well fix this.
>
> - Don
>
>
> On Thu, 2006-12-07 at 12:12 -0500, Don Dailey wrote:
> > On Thu, 2006-12-07 at 16:05 +0100, Łukasz Lew wrote:
> > > ii = pm::rand () % empty_v_cnt; // TODO improve speed "%"
> >
> >
> > Try this, I think it could be faster, not sure, but has the advantage
> > that it's slightly more correct.
> >
> > // returns an integer between 0 and n-1 inclusive
> > //
> > unsigned long randint(unsigned long n)
> > {
> > unsigned long v = n;
> > unsigned long r;
> >
> > v--;
> > v |= v >> 1;
> > v |= v >> 2;
> > v |= v >> 4;
> > v |= v >> 8;
> > v |= v >> 16;
> >
> > do { r = rand(); } while ( (r & v) >= n );
> >
> > return( r & v );
> > }
> >
> >
> >
> > - Don
> >
> >
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>
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