2.08 and Incompatible Battle Reports

[Saber Cherry]

Yay! Not only was the problem solved, but also, Microsoft gets another black mark

[PhilD]

Originally posted by Johan K:
Some good new for those who don't play Dominions on Windows exclusively. The problem with incompatible battle replays has been found. There was a disagrement on how to compile an expression between microsoft's and the others' compilers.

Magic resistance check:
if (penetration+2d6 < MR+2d6)

Other compiler solved it from left to right, but microsoft's solved it from right to left. This results in the same roll of dice appearing on different sides of the '<' for windows and linux.
Bloody annoying!


Alexti: Thanks for the STL info and I use MSVC6.

Hmm... it's been some time since I had a look at books where the norm is described, but I'm not sure it says anything for this. I believe the result is "unspecified"...

Don't use two function calls in the same expression, is the lesson.

(And congrats on the Illwinter crew! When are we getting a patch so we can celebrate?)

[fahdiz]

Originally posted by PhilD:
(And congrats on the Illwinter crew! When are we getting a patch so we can celebrate?)

I second on both counts. After reading Arryn's AAR, Utgard is calling to me...

...unfortunately, it's calling from a moose-laden Smouldercone right now.

[Saber Cherry]

Originally posted by PhilD:
Don't use two function calls in the same expression, is the lesson.

Compliers do strange things. A poorly-written compiler could rearrange consecutive lines if there is no obvious dependancy.

1: a=2d6+penetration
2: b=2d6+mrst
3: if(a>b){do c}

Lines 1 & 2 could be rearranged by a compiler if, for example, mrst is more local (already in a register) and penetration has to be fetched. That would have the same effect. I think C has some commands that let you force the complier to not rearrange things, though.

So the moral is actually not to trust Microsoft products, since they take away your control

[Taqwus]

There may be #pragmas or compiler options to change reordering behavior, but I'm not too familiar with MSVC.
Wrapping the randomizer in an object and making sure that the "get a random number" method (perhaps as a static method, even) might serve as a hint to the compiler; could be more work than it's worth.

[edit] Making sure that it's not flagged as constant, that is. IOW to encourage the compiler to consider side-effects of function invocation.

[ February 25, 2004, 18:51: Message edited by: Taqwus ]

[Pocus]

I have often battle inconstancies message now, with solo play on windows platform.

[Gandalf Parker]

Way outside of my area but I was thinking that the Devs might have to write their own randomizing routine, and have the host create a seed. Then pass the seed its using inside each of the player files so that the players copy of Dom would definetly use the same routine on the same seed. I never figured on different OSs doing standard math in different orders. Thats insane.

[ February 25, 2004, 18:58: Message edited by: Gandalf Parker ]