Which would make 15 the highest possible instead of 24? To make it (random between 1 and 5) times 3Īs opposed to (random between 1 and 8) times 3 I've never even used & or any bit type stuff in any python program, which feels like I'm missing out on the heart of programming.įunny reading the doom wiki how simple p_random() is, just a shuffled list (basically, some digits missing, some repeated) of 0-255 and it increments through linearly.Ĭouldn't the playstation code just add a '-3': I almost got into c, but installing SDL took so many steps I was put off.ĭo you know if modulus is 'expensive' in python too? I use it quite a lot. Python, which I use, hides all this byte stuff seemingly which kind of sucks. Oh, I get it, the purpose of the 7 is to pack 0s at the left to change a bigger random number of 0-255 into a random number of a smaller range, 0-7 (+1 though, so 1-8). That means if both 1s are 1, its a 1 otherwise its a 0 so: So p_random() returns a number from 0-255, say it returns 254, I assume it returns 254 as a byte like this: That means you're in the 'danger zone' as soon as you drop below 25 health in PSX Doom, which is pretty brutal when you also consider the sheer volume of hitscanners they added in UV >_>

In this case though it has the side effect of creating a much wider range of possible values, AND a fairly significant increase in max possible damage - from 15, to 24. So to buy CPU cycles, it makes sense, where possible, to replace it instead with an 'and' with the nearest multiple of 2 minus one, because such and ops, which are VERY fast on just about all hardware, behave just like a modulus. Modulus, if it was even available as an instruction on the Jag's hardware in the first place, would be one of the most expensive instructions. In the original PC, the calculation is ((P_Random()%5)+1)*3.

What we've found so far (I and others) is that these calculations were changed in Jag Doom, and the reason they were changed was to avoid mul and mod instructions. That seems to be what's happening here as well. I think most damage values in vanilla were calculated by setting a primary damage value and then randomly multiplying it anywhere from 1x to 8x per hit. Well, those damage values aren't particularly abnormal.

Ida pro psx