Rust 溢出检查连续更多的整数运算

Question

How can I do overflow check in all steps of a

fn somemath() -> u32 {
   let x: u32 = y * 3 + 2;
   return x
}

something similar to

fn somemath() -> u32 {
    let x: u32 = y.checked_mul(3).checked_add(2)
    return x
}

Or what is the best practice, to avoid overflow in such cases? In the end I need x to be not producing overflow and be a valid result or produce error and can the function return u32 if successfull?

Answer 1

It's up to you to decide whether the check is necessary, and what do do when it overflows.

If there's no meaningful result if the overflow happens, you can return Option::None for example:

fn somemath(y: u32) -> Option<u32> {
    let x: u32 = y.checked_mul(3)?.checked_add(2)?;
    return Some(x);
}

fn somemath(y: u32) -> Option<u32> {
    y.checked_mul(3)?.checked_add(2) // same, but shorter
}

You could also check whether inputs are small enough that overflow will never happen. Or you could use a larger type for intermediate values (eg u64 here) to get a valid result for any u32 input.