Best (CD Bootable?) Linux Distro for Dominions?

Johan K · #1 March 25th, 2004, 10:25 PM

The source of the bug has been discussed in another thread. It's called battle inconsistency.... something. Anyway it was a compiler inconsistency.

Gandalf Parker · #2 March 25th, 2004, 11:11 PM

Quote:

Originally posted by ywl:

quote:
Originally posted by Johan K:
This bug has been fixed in the next patch. So hopefully you'll soon be able to mix OSes and still get correct battle replays.

Just curious. What's the source of the bug?

It was something about the windows compiler not doing math formulas in quite the same order as generic open OS compilers.

PhilD · #3 March 25th, 2004, 11:22 PM

Quote:

Originally posted by Gandalf Parker:

quote:
Originally posted by ywl:

quote:
Originally posted by Johan K:
This bug has been fixed in the next patch. So hopefully you'll soon be able to mix OSes and still get correct battle replays.

Just curious. What's the source of the bug?
It was something about the windows compiler not doing math formulas in quite the same order as generic open OS compilers.

More precisely, I believe, it was the Windows compiler doing things correctly, but differently than other compilers, with code that is somewhat ambiguous.

Not everything is Microsoft's fault, after all.

Gandalf Parker · #4 March 26th, 2004, 12:10 AM

Quote:

Originally posted by PhilD:
It was something about the windows compiler not doing math formulas in quite the same order as generic open OS compilers.

More precisely, I believe, it was the Windows compiler doing things correctly, but differently than other compilers, with code that is somewhat ambiguous.

Not everything is Microsoft's fault, after all.

I agree. I use Windows most of the time and consider it great for some things. I didnt say it did it wrong, I just said it did it differently than the multi-OS compilers did.

[ March 25, 2004, 22:12: Message edited by: Gandalf Parker ]

Cainehill · #5 March 26th, 2004, 12:16 AM

Quote:

Originally posted by Gandalf Parker:
It was something about the windows compiler not doing math formulas in quite the same order as generic open OS compilers.

Which is of course why (in C/C++ especially) explicit grouping (via parenthesises) is your friend. Makes it easier for the human programmer to know exactly what the code is going to do, and makes it harder for evil compilers to find wriggle room to twist the programmer's intent.

alexti · #6 March 27th, 2004, 01:10 AM

Quote:

Originally posted by Cainehill:

quote:
Originally posted by Gandalf Parker:
It was something about the windows compiler not doing math formulas in quite the same order as generic open OS compilers.

Which is of course why (in C/C++ especially) explicit grouping (via parenthesises) is your friend. Makes it easier for the human programmer to know exactly what the code is going to do, and makes it harder for evil compilers to find wriggle room to twist the programmer's intent.

I'm curious. Is it possible to fix Johan's problem with just grouping by parenthesises? How would you rewrite the expression for that?

Cainehill · #7 March 27th, 2004, 02:49 AM

[quote] alexti:
[QB]I'm curious. Is it possible to fix Johan's problem with just grouping by parenthesises? How would you rewrite the expression for that? [\qb]

Well, if "It was something about the windows compiler not doing math formulas in quite the same order as generic open OS compilers" then odds are that the use of parathensises, and breaking the formula down into discrete lines of code, would take care of it.

Hard to say how to rewrite the expression without seeing the source code and expression, but the complex multiline statements often used to express formulas are a common source of problems. The C++ standard left a few too many things (like order of evaluation) undefined, meaning that even on the same platform, different compilers give different results. This is even without accounting for compiler inadequacies, where there is currently only one (Comeau / EDG) available that is approximately 100% compliant with the standard. (Last I knew, Comeau didn't support "export" on templates, but then, no one does.)

Another likely culprit, though, would be automatic promotion of floats to doubles - different compilers handle it differently, leading to some wildly disparate results. Again, often best handled through explicit casting, and breaking long statements into short ones, such that intermediate results aren't left to compiler whims.

Anyways - use of parenthesises, and breaking complex lines of code (especially calculation heavy code) down into shorter, simpler, statements makes multiplatform life _much_ easier.

Cainehill (whose Last job involved a lot of graphics, GUIs, and modeling & simulation with the same source on different hardware platforms and OSs)