Tracking Issue for "widening" multiplication methods

[clarfonthey]

Feature gate: #![feature(bigint_helper_methods)] (for now)

This is a tracking issue for the widening_mul methods on integers.

Public API

impl uN {
    const fn widening_mul(self, rhs: uN) -> (uN, uN);
}
impl iN {
    const fn widening_mul(self, rhs: uN) -> (iN, iN);
}

Steps / History

(Remember to update the S-tracking-* label when checking boxes.)

• Previous tracking issue Tracking Issue for bigint helper methods #85532
• Final commenting period (FCP)

Unresolved Questions

• The return type of this method is the main concern.

[Amanieu]

We discussed this in the @rust-lang/libs-api meeting while discussing rust-lang/libs-team#738. We would like to see widening_mul return a wider integer type instead of a pair of integers, and simply not have these methods available on 128-bit integers. This is what makes the most sense given the method name.

[clarfonthey]

I think that's extremely fair, given the fact that this is technically available via carrying_mul on 128-bit integers anyway, as long as you pass zero for the carry.