Rename libafl_bolts::rands::Rand::zero_upto to below_or_zero.

[Railroad6230]

Hi LibAFL!

I was playing with the Rand trait when I realized that the
documentation of Rand::zero_upto did not match what I was expected:

LibAFL/libafl_bolts/src/rands/mod.rs

Lines 139 to 142 in fd6271f

	/// Gets a value between [0, n]
	fn zero_upto(&mut self, n: usize) -> usize {
	fast_bound_usize(self.next(), n)
	}

When using the following RNGs, Rand::zero_upto never returns the upper bound n as it would have been expected according to the documentation:

• RomuDuoJrRand
• RomuTrioRand
• Sfc64Rand
• XkcdRand
• XorShift64Rand
• Xoshiro256PlusPlusRand

The default implementation of Rand::zero_upto is to use fast_bound_usize,
which excludes the given upper bound, thus I believe here that the default implementation
of Rand::zero_upto is wrong.

As discussed here: #2911 (comment),
we believe that renaming the method would be better than changing the actual
implementation.

[tokatoka]

i think the correct thing to do is to fix the doc, by changing it to [0, n)

[tokatoka]

i put this function because it is a better alternative than the below function so when i coded it i expected it not to include n.
if you include n then i think it'll break some code in other parts (as the ci failures suggest)

[Railroad6230]

if you include n then i think it'll break some code in other parts (as the ci failures suggest)

I was thinking of the same thing as well, but wouldn't it mean that we should also change the function's name?

I'm far from being a native english speaker, but I think that in math, up to means that the upper bound is included, and less than means that it is not.

What do you think?

[tokatoka]

you can change it to zero_upto_excl() or anything if you have better idea of names.

[tokatoka]

i'm fixing ci. and merge to your branch later

[Railroad6230]

you can change it to zero_upto_excl() or anything if you have better idea of names.

Sounds good to me.

I've renamed it and I've reverted my changes in the default implementation.

Thank you for your feedback!

[domenukk]

Wait, this gets super confusing.
[0, n[ would not include 0 if n == 0(?)
how about naming this below_or_zero?

[tokatoka]

good for me

[Railroad6230]

Wait, this gets super confusing. [0, n[ would not include 0 if n == 0(?) how about naming this below_or_zero?

sounds good to me as well.

Fixed in 3b31a18