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crystal-lang

How to do an unsafe addition (addition without throwing OverflowException) in Crystal?

How do I able to add Int::MAX + 1 without getting OverflowException? I know I can do

def add_unsafe(a : Int, b : Int) : Int
    ((a.to_i128 + b.to_i128) % Int32::MAX).to_i
end

But is there any alternative to do this?

Solution

  • You're looking for wrapping operators. Most math operators have a wrapping variant prefixed with &. So in your case, that would be a &+ b.

    Btw. your example doesn't work because to_i still does an overflow check. So calling add_unsafe(Int32::MAX, 1) raises an error. A more accurate representation of wrapping behaviour would be (a.to_i128 + b.to_i128) % Int32::MAX. The &+ operator is obviously better, though.