`unchecked_wrapping_rem` and `checked_wrapping_rem` for `iN`

[Apersoma]

Proposal

2 methods,unchecked_wrapping_rem and checked_wrapping_rem, for computing the remainder of 2 signed ints that return 0 for iN::MIN % -1 and have UB or return None for on division by 0 respectively.

Problem statement

Remainder functions and their variants being fallible at iN::MIN % -1 is rarely expected behavior and very often unwanted. Far more so than the failure condition for any other operator since the answer exists and does fit in the type.

Motivating examples or use cases

Almost always when wanting a remainder op that doesn't panic on div by zero, would these variants be preferable to the variants of the regular remainder op.

Solution sketch

const fn checked_wrapping_rem(self, Self) -> Option<Self>;
unsafe const fn unchecked_wrapping_rem(self, Self) -> Self;

Alternatives

Manual implementation via if else or bool.then for checked_rem or implementation via assert_unchecked for unchecked_rem. These could not be implemented as methods without having to be non-const because of limitations on traits.

Links and related work

#526
#774

What happens now?

This issue contains an API change proposal (or ACP) and is part of the libs-api team feature lifecycle. Once this issue is filed, the libs-api team will review open proposals as capability becomes available. Current response times do not have a clear estimate, but may be up to several months.

Possible responses

The libs team may respond in various different ways. First, the team will consider the problem (this doesn't require any concrete solution or alternatives to have been proposed):

• We think this problem seems worth solving, and the standard library might be the right place to solve it.
• We think that this probably doesn't belong in the standard library.

Second, if there's a concrete solution:

• We think this specific solution looks roughly right, approved, you or someone else should implement this. (Further review will still happen on the subsequent implementation PR.)
• We're not sure this is the right solution, and the alternatives or other materials don't give us enough information to be sure about that. Here are some questions we have that aren't answered, or rough ideas about alternatives we'd want to see discussed.

[pitaj]

Assuming typo your solution sketch has two unchecked

[Apersoma]

Assuming typo your solution sketch has two unchecked

fixed