Add new C++ Random functions to replace old C ones.

[Nakhr11n]

Pull Request Type

• [ ] GitHub Workflow changes
• [ ] Documentation or Wiki changes
• [ ] Build and Dependency changes
• [x] Runtime changes
  • [ ] Render changes
  • [ ] Audio changes
  • [ ] Input changes
  • [ ] Network changes
  • [x] Other changes

Description

There are three uses of randomness in the codebase:

• to get a random int within a range.
• to get a random float within a range.
• in if statements to do things x% of the time.

In all cases some variant of the C rand() function is used. In many cases this results in code that is very hard to read, which makes it difficult to understand in what range the randomness will lie.

I propose to add these three functions which add modern C++ equivalents to rand() for the three use cases. The new functions are faster, safer and clearer.

My thinking is to then go over the code and replace all uses of randomness with these functions, and then remove misc/psrand.cpp and lib/psrand.h.

Related Issues

Screenshots (if applicable)

Checklist

• [x] I have tested my changes locally and verified that they work as intended.
• [x] I have documented any new or modified functionality.
• [x] I have reviewed the changes to ensure they do not introduce any unnecessary complexity or duplicate code.
• [x] I understand that by submitting this pull request, I am agreeing to license my contributions under the project's license.

Additional Comments

[bryanperris]

Is this still work in progress, if so, can you make a draft instead?

[Nakhr11n]

@bryanperris My thinking was to gauge interest with this initial PR. And then to submit follow-up PRs that actually replace the old random code.

Should I split it up, or should I do everything in this PR?

[winterheart]

I'd recommend place it to misc directory and then reuse it as part of misc module. In that way we can gracefully replace old psrand() generator.

Please note, that psrand implementation uses some magic numbers on generating "random" numbers:

int32_t ps_rand(void) { return (((ps_holdrand = ps_holdrand * 214013L + 2531011L) >> 16) & 0x7fff); }

I cannot say if this really used in order to receive predictable random sequences, but it would be great if we somehow preserve this approach.

[bryanperris]

We can keep this to a single PR

[GravisZro]

Personally, I prefer the simplicity of srand and rand. Also, I found these when working on RAND_MAX overflow issue:

• qRandomChance
• qRandomValue

If you can make the existing D3 code more readable with some function shortcuts then I'm in favor of it though I'm not sure the PRNG needs work. From what I can tell, the existing code (ps_rand) is simplified explicitly to be faster than the lib C rand.

[Lgt2x]

Have you investigated the use cases of random functions in the game? I'm afraid that changing random functions used (and thus potentially distribution of values) could have side-effects affecting game play that are difficult to predict.