All bit twiddling functions in num::traits::PrimInt should take or return usize instead of u32

[octurion]

The trait num::traits::PrimInt mandates that any type implementing it must also implement Shl<usize, Output=Self> and Shr<usize, Output=Self> (in other words, PrimInt mandates that the shift amount be of type usize).

Thus all bit twiddling functions (trailing_zeros, rotate_left, count_zeros etc.) in PrimInt should take or return a usize instead of u32 as the number of bits for the sake of consistency with what the implementation restrictions on Shl and Shr mandate.

[gnzlbg]

The problem is that the methods on primitive types like rotate_left expect an u32 and that cannot be changed anymore (that ship has sailed).

Maybe it would be better to require Shl<u32, Output=Self> and Shr<u32, Output=Self> instead. What do you think?

[gnzlbg]

I've implemented this and some other bit wise algorithms in PrimInt.

[cuviper]

I think changing the trait bounds to u32 sounds fine, but it will be a breaking change, which I want to be pretty conservative about. I should start a list somewhere of "things to break" so we can plan to do them all at once.

[cuviper]

This issue was moved to rust-num/num-traits#14