Have in mind that having a 64 bit executable it's going to be always slower than a 32 bit one for a simple reason, memory pointers are 64 bits and not 32, so just to start, you'll have to move twice the data from memory to CPU. Since most of the code uses just 32-bit values, it's not really worth switching to 64 bits, there is no other advantage in doing so.
Plus, as already said in this post, there are many optimizations in code and data structures that assume 32-bit, forcing a 64 bit build will neutralize this optimizations. The only advantage it can have is allowing bigger maps in simutrans, for the case memory usage aproaches 2Gb, but at those sizes, simutrans does not perform too well anyway.
It's been some time I don't look at current chips specifications, and it might be that even loading a 32-bit value from memory just fetches 64 bit instead anyway and cache the not used part in the CPU cache, but anyway even in this case a array of pointers (there are many in simutrans), will have double the size in 64-bit than in 32-bit, making the cache perform worse.
As to contribute: I'm not really much attached to development in simutrans now, I'll maybe come back to contribute code when I get excited about something I want to do, but iirc there were many open aspects of the code that needed improvement, and features that could be implemented. prissi/dwachs will maybe point you there as soon as they can. But I have some suggestions that you might find useful:
- Maybe you can explore the scrpiting system in simutrans (squirell) to make a interactive new players "tutorial of first steps", like "ok, build a road from here to here, ok, buiy a vehicle, ok, set schedule, ok, go, watch finance window... " . Just an idea. This is not so easy, because you might to implement or ask to implement some new UI functions like highlight GUI buttons, or mark in a special way the map and so no.
- You can try to fix the bugs posted in the forum and try to fix yourself (I think there are some still open)
- You can check the list of extension requests that are floaring around this forum and try to work on one of your choose.