Many of you have claimed meteor defenses don't always fire at EMP missile in multiplayer. I decided to go looking and found that there is indeed a case when the meteor defenses won't fire. There is about a 1/8 chance of this happening.
What causes this to happen is the checks for when an EMP missile is shot down only run when the count down until impact is strictly between 12 and 20. But the function that performs these checks is called by another function which only executes it's body of code every 8 ticks. As you can see, there are only 7 numbers strictly between 12 and 20. {13, 14, 15, 16, 17, 18, 19}
What happens then is if the timing lines up nicely, then the missile count down timer goes from 20 to 12, without ever hitting any of the intermediate values, and so the code that checks for meteor defenses shooting them down is never run.
What can make this potentially worse, is that the command packet execution granularity is 4 ticks. Which means that 1/8 chance can become a 1/2 chance under the correct conditions (or no chance under different conditions).
If someone is exploiting this vulnerability against you, you can try to stop that by changing the number of units in the game. That is, build an extra unit, or get rid of one. It should offset the timing requirements, and change that 1/2 into a 0. At least until any of the players undo that change in the number of units.
I've attached a test DLL that demonstrates the bug. I'm leaving out the source on this one though. I'm sure some people would purposefully exploit this in multiplayer if they knew how.
You can control the AI Spaceports by moving your scout between the different markers. The meaning of each marker is given as in game messages, and it'll tell you when the AI state is updated.
