Implement Pow for BigUint and BigInt

[clarfonthey]

See rust-num/num-traits#38 for details on this trait.

[vks]

Is this necessary given that it is implemented in num-traits now?

[cuviper]

What do you mean? Pow is defined in num-traits, and implemented for the primitive types, but we need to implement it here for bigints.

[vks]

I thought num-traits provided a generic implementation, but apparently that is not the case.

[thomwiggers]

Let's see if I can do this – I need in anyhow.

[vks]

@cuviper I found it: num_traits::pow. This should work for BigInt as well. (Something like powm in this num-integer PR would probably be more efficient though.)

[cuviper]

I found it: num_traits::pow. This should work for BigInt as well.

Yes, but that only works by-value with a usize exponent. The Pow trait is more flexible.

(Something like powm in this num-integer PR would probably be more efficient though.)

Modular pow is a different thing though -- and FWIW we do have inherent modpow methods here.

[vks]

Yes, but that only works by-value with a usize exponent. The Pow trait is more flexible.

A u32 exponent should be enough, and by-value is more efficient.

[windelbouwman]

I'm interested in this pow function, will there be a new release of this crate at some point containing pow, or is there work left to do?

[cuviper]

Thanks for the reminder - I've published num-bigint 0.2.1.

[peterbraden]

Still not updated in num? I get:
Updating crates.io index Downloading num v0.2.0 Downloading num-bigint v0.2.1 Downloading num-rational v0.2.1 Compiling num-integer v0.1.39 Compiling num-iter v0.1.37 Compiling num-complex v0.2.1 Compiling num-bigint v0.2.1 Compiling num-rational v0.2.1 Compiling num-bigint v0.1.40 error[E0277]: the trait boundbiguint::BigUint: num_traits::Num is not satisfied

[cuviper]

@peterbraden Somehow you have both new and old, Compiling num-bigint v0.2.1 and Compiling num-bigint v0.1.40. Only 0.2.1 implements Pow.

Your output doesn't show which num-traits you're compiling, but your two num-bigints will also require num-traits 0.2 and 0.1. That would be OK for Num (your error message) if the latter were 0.1.43, as that just re-exports the 0.2 versions. Alternatively, num-bigint 0.1.41 started using num-traits 0.2 as well, but it still won't have Pow.

[peterbraden]

I did a cargo update and all worked, not sure how I got into that state, thanks!