Allow constructing generators from `rand_xoshiro` without checks for 0

[Shatur]

It would be nice to have a way to avoid checks like this:

rngs/rand_xoshiro/src/xoroshiro128plusplus.rs

Line 87 in 2100f8f

deal_with_zero_seed!(seed, Self, 16);

My use case is embedded development, and this check increases the code size. Since my seed comes from a hash function, I know it won't be zero.

Right now I simply vendor my own Xoshiro128PlusPlus from the C implementation because of this, but it would be nice to just use the well-known crate directly.

[dhardy]

Since my seed comes from a hash function, I know it won't be zero.

With a 1-in-2^128 chance of failure: insignificant for most purposes. It's nice not to have to make assumptions like this in general, especially since the failure mode for seed zero is so bad.

this check increases the code size

And this is significant?

I guess we could add an alternative constructor (not using SeedableRng).

[Shatur]

I don't remember the exact numbers, but I remember it was high according to cargo bloat. Of course it's all relative - our code is quite small 🙂 We were tight on code size and tried to reduce it as much as possible.

I guess we could add an alternative constructor (not using SeedableRng).

Yes, having a non-trait constructor that accepts 2 numbers would be perfect! (with a huge warning!)

[dhardy]

A minimal addition with clear documentation should be acceptable if you'd like to make a PR.