Guide page for generating seeded random floats

[Harnesser]

Hi all,

I'd love to see recipe page on the best way to generate seeded random floats for procedural generation applications.

This request comes from a recent unsuccessful experience I had trying to upgrade from 0.3 to 0.6 of rand. My 0.3 code uses a {SeedableRng, from_seed(), next_f32()} recipe I found on the web somewhere that's not suitable for 0.6, plus a --seed command line option to set the seed.

• Do I need to use from_seed_u64() now?
• Do I need to implement a trait on a typedef like in the tests?
• Do I need to add rand_core as well as the usual rand to Cargo.toml.
• Do I need to decide on a PRNG? Can you suggest a suitable one for procedural generation work?

Thanks!

[dhardy]

Is this what you want?

Sorry, I don't quite follow. If you know how to improve the documentation though, a contribution would be very welcome!

To answer your bullet points:

• SeedableRng::seed_from_u64 is the easiest way to seed from an integer
• Don't know what you mean here; you can't implement traits on typedefs anyway. You do have to "use" (import) traits.
• No; all the bits of rand_core (other than utilities for implementing new RNGs) are availble in rand too
• Yes, you should decide on a PRNG. Probably any of the ones we have are suitable for procedural generation, crypto or not (the main difference being crypto ones use more memory and batch their generation). If you want reproducible generation across library versions, then don't use SmallRng / StdRng; you may want to look at the rand_xoshiro and rand_pcg crates (first one isn't published yet but hopefully will be later today)

[dhardy]

It's also worth noting that using gen_range or the Uniform distribution may be a little faster and more accurate than using gen() and modifying/shifting the result. Here's an expanded example.

[Harnesser]

Thanks - the first example was especially useful!

I would have like to have found a "recipe" page in the docs with:

• the above example
• some of your remarks above
• and maybe notes on re-seeding in an interactive application
• with links to more in-depth section in the rand-book

I'd like to have a go at creating such a page for documentation, as thanks for your help. I'm not sure if the page would be best in the rand book, or in the main Rust Cookbook. What do you think?

Thanks again!

[dhardy]

I'm not sure if the page would be best in the rand book, or in the main Rust Cookbook. What do you think?

Depends where people are more likely to look for such documentation?

The book as it stands was written fairly quickly to at least have some doc beyond the API. It could certainly be expanded significantly. I can't gauge what content all readers want and also don't currently want to contribute new content to the book myself, but if you would like to I would be happy to review.