rust - Is there a modulus (not remainder) function / operation?

Question

In Rust (like most programming languages), the % operator performs the remainder operation, not the modulus operation. These operations have different results for negative numbers:

-21 modulus 4 => 3
-21 remainder 4 => -1

println!("{}", -21 % 4); // -1

However, I want the modulus.

I found a workaround ((a % b) + b) % b, but I don't want to reinvent the wheel if there's already a function for that!

Answer 1

RFC 2196 adds a couple of integer methods related to euclidian division. Specifically, the rem_euclid method (example link for i32) is what you are searching for:

println!("{}", -1i32 % 4);                // -1
println!("{}", (-21i32).rem_euclid(4));   // 3

This method is available in rustc 1.38.0 (released on 2019-09-27) and above.