Check if PrimInt is even or not

[matthew-hennefarth]

Is there any neat way to check if a primitive integer is even or odd? Currently I would imagine either some casts or some bit-wise manipulations on the generic type PrimInt is needed and it would obfuscate code readibility. For example, if we used the modulo way:

fn some_func<T>(n: T) -> bool
where 
    T: PrimInt + FromPrimitive,
{
    // Do something else...
    n % T::from_usize(2).unwrap() == T::zero()
}

versus something like

fn some_func<T>(n: T) -> bool
where 
    T: PrimInt + FromPrimitive,
{
    // Do something else...
    n.is_even()
}

Thoughts? I could work on a PR if this would be appreciated.

[cuviper]

Those methods do exist more generally on Integer, so I'd be wary of adding ambiguity if PrimInt got the same.
https://docs.rs/num-integer/latest/num_integer/trait.Integer.html#tymethod.is_even

To do it yourself, PrimInt includes Shl/Shr<usize>, so you can use ((x >> 1) << 1) == x for even.
https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=02fcdb7c587a5a6b86c74400e7b476d4

[matthew-hennefarth]

Thanks! Makes sense to not have it in both Integer and PrimInt since it can cause conflicts.

[cuviper]

Another option is n.trailing_zeros() > 0. On x86_64, it's optimized to the same bit test either way.