How can integer overflow protection be turned off?

Question

My default Rust has integer overflow protect enabled, and will halt a program in execution on overflow. A large number of algorithms require overflow to function correctly (SHA1, SHA2, etc.)

Answer 1

Use the Wrapping type, or use the wrapping functions directly. These disable the overflow checks. The Wrapping type allows you to use the normal operators as usual.

Also, when you compile your code in "release" mode (such as with cargo build --release), the overflow checks are omitted to improve performance. Do not rely on this though, use the above type or functions so that the code works even in debug builds.

Answer 2

Francis Gagné's answer is absolutely the correct answer for your case, but there is a compiler option to disable overflow checks. I don't see any reason to use it, but it exists and might as well be known about:

#![allow(arithmetic_overflow)]

fn main() {
    dbg!(u8::MAX + u8::MAX);
}

Via Cargo

Set this in your profile section:

[profile.dev]
overflow-checks = false

% cargo run -q
[src/main.rs:6] u8::MAX + u8::MAX = 254

Via rustc

Use the -C overflow-checks command line option:

% rustc overflow.rs -C overflow-checks=off

% ./overflow
[overflow.rs:6] u8::MAX + u8::MAX = 254