Incompatible battle replays across OSes

PhilD · #1 January 12th, 2004, 09:58 AM

In my first email game, I had the same problem twice: the battle replay I watched (on a Linux machine) was very different from the one announced in the Messages. The second time around, I took the time to watch the replay under Windows, and it was much more accurate.

This seems to indicate that the method used to store the replays is NOT compatible across platforms. I'd heard of replay errors before, but if my guess is correct, this will most probably kill my enjoyment of PBEM; I believe it's a serious bug.

I've read that the .trn files only store the random generator seeds, and the replays are recalculated by the game. If so, then it might be a simple inconsistency in random number generators, and reasonably easy to fix (add the same random number generator to all Versions instead of using libraries that might be incompatible).

Did anybody else notice this trend? I suppose most players are using Windows, but there must be a reasonable number of Linux/MacOS/Solaris Users too...

Saber Cherry · #2 January 12th, 2004, 10:21 AM

Yes, it is VERY annoying!!! Watching your troops win a glorious victory, then looking at the casualty list to see that you actually lost, and all your leaders were killed. I didn't realize the problem was OS differences. Dumb C - that's why I like Java. Well, one reason.

-Cherry

PDF · #3 January 12th, 2004, 10:53 AM

Hi Phil,
The OS "bug" would explain the strange things we observed in our game replays indeed

Did you notice oddities in the Last turn's battles ? I was present in 3 of them and observed another between you and Abysia. On my Win machine the battles were consistent with the results (on the first battle the end of the battle was quite strange, with your winning troops suddenly all killed ...).
Anyway you should send the trn files to IW people so they examine what happens.

Johan K · #4 January 12th, 2004, 12:35 PM

The OS inconsistency is not related to the random number generator (hopefully) as Dominions uses its own random number algorithm. But something sure seems to be weird.

Pocus · #5 January 12th, 2004, 03:10 PM

and cant it be related to the rounding of some results, which would vary depending of the OS or the processor. Dunno how your algorithm works, but if it takes for example the 25th decimal of a number at a given time, like say

ln(0.123456789)
=
-2.091864070778393122967989 *7* 441961
on windows (being 7 there)
then perhaps it will be slightly different in linux.
?

Johan K · #6 January 12th, 2004, 06:36 PM

The random number generation itself should be foolproof. Only table lookups and some xor. Unfortunatelly the random number generation is only 0.0001% of what might go wrong, so your idea might still have some merit. The battles use sinus (sinf()) calculations and those might just be bad if those calculations should be significantly differnt on different machines. Definitely worth some thought...