Contribute is_power_of_ten?

[mohrezaei]

I'd like to contribute a high performance implementation of is_power_of_ten. Is that an appropriate function for this crate?

[cuviper]

I'm open to it, if we can present it in a generic trait befitting the rest of the crate. That doesn't mean that you have to have a generic implementation, just that it's designed such that things like BigUint can implement it too. Take the Roots trait, for example.

The unsigned primitive integers already have is_power_of_two, and a related next_power_of_two. It would be good to also abstract this in a trait, while we're doing it for 10. Something like:

pub trait Power2: Integer {
    fn is_power_of_two(&self) -> bool;
    fn next_power_of_two(&self) -> Self;
}
pub trait Power10: Integer {
    fn is_power_of_ten(&self) -> bool;
    fn next_power_of_ten(&self) -> Self;
}

Or maybe just combine those into a single trait Powers. And feel free to suggest a better name.

Could we reasonably implement checks for arbitrary powers of n? It wouldn't have to be as fast, but I'm wondering if that's feasible and useful to have too.

[cuviper]

Floored log2 and log10 might also fit into the scope of this design.

[mohrezaei]

A separate trait is consistent with the way I was thinking about it.

Curious, why don't signed primitive integers implement is_power_of_two? (obviously, all negative numbers would return false).

How would we abstract over arbitrary powers on n? Extra parameter to the method? I think 2 and 10 are sufficiently interesting to have their own trait.

[cuviper]

Curious, why don't signed primitive integers implement is_power_of_two? (obviously, all negative numbers would return false).

I'm not sure, but probably just because negative inputs are useless if they're all false.

Similarly, what would next_power_of_two do with a negative -- jump all the way to 1?

How would we abstract over arbitrary powers on n? Extra parameter to the method?

Yeah, fn is_power_of_n(&self, n: u32) -> bool, or maybe n: usize or n: &Self. I'm not sure if this is really useful anywhere, just musing.

[mohrezaei]

Alright, that gives me enough to move this over to a PR. Expect something in the next few days. :smile: