Starcraft AI blog

Last year, Steamhammer finished SSCAIT for the first time with no losses due to crippling bugs and only 2 close calls. So far, it is on track to repeat in this year’s SSCAIT. I have seen all its games up to now, and there are no losses due to egregious bugs (only the standard issue flaws) and only one near miss. That’s great compared to Steamhammer’s early years, but I still want to fix the bugs.

The bad game is Steamhammer vs legacy (random zerg). Steamhammer made a number of mistakes in the game and suffered at least 2 bugs. The bug I could not accept is that it built spore colonies to defend against air attack—very early, immediately after scouting legacy’s base and seeing that it had not yet taken gas. It’s not possible to get mutalisks that fast, and without gas there was not even a hint of future risk. In fact, legacy never took its gas and played the whole game with a mass slow zergling plan. If Steamhammer had held on to the drones instead of wasting them on static defense due to a bug, I doubt the attack would have troubled it at all.

I traced the bug to, of all things, an integer overflow. The routine that figures out the time the enemy’s spire will complete returns INT_MAX for “never” if there is no evidence of an enemy spire... and I brilliantly added a margin for the mutas to hatch and fly across the map. In C++, integer overflow is officially undefined, so the compiler retreats to its room and laughs its head off before generating the code that will cause the most possible confusion, because “undefined” means it can do that. I don’t know what it did this time, but it was not as simple as wrapping around from an extreme positive value to an extreme negative value, because that would have caused the bug to show up in half of ZvZ games. No, it’s better if it shows up only when it will cause a disgusting blunder out of nowhere.

Anyway, it was easy to fix. I also fixed a bug that caused multiple commanding of overlords. And I’m writing code to collect data for my main current project. Progress is underway.