CODEWITHSUNDEEP
rustinteger-overflow
eonil
eonil

Reputation: 85975

How do I return a flag on integer overflow in Rust?

Swift has integer overflow arithmetic functions which return a flag whether the number has overflowed or not. Do we have same thing in Rust?

Upvotes: 12

Views: 4753

Answers (3)

eonil
eonil

Reputation: 85975

Rust has integer arithmetic intrinsics such as add_with_overflow.

pub unsafe extern "rust-intrinsic" fn add_with_overflow<T>(
    x: T, 
    y: T
) -> (T, bool)

Upvotes: 5

Danilo Bargen
Danilo Bargen

Reputation: 19432

Since Rust 1.7.0, there's overflowing_<operation>(rhs) defined on integer types.

Example for overflowing_add:

Calculates self + rhs

Returns a tuple of the addition along with a boolean indicating whether an arithmetic overflow would occur. If an overflow would have occurred then the wrapped value is returned.

Example:

use std::i64;

assert_eq!(5i64.overflowing_add(2), (7, false));
assert_eq!(i64::MAX.overflowing_add(1), (i64::MIN, true));

(playground)

Upvotes: 20

huon
huon

Reputation: 102056

As you note, there are intrinsics for this but these are unsafe and somewhat annoying to use.

Before Rust 1.0, the standard library provided wrappers that detect the overflow for the 4 arithmetic operations in the form of CheckedAdd, CheckedSub, CheckedMul and CheckedDiv.

As of Rust 1.0, these traits no longer exist and there are just inherent methods on each numeric type, such as i32::checked_add.

However, these just detect overflow and do not return the overflowed-result:

fn main() {
    println!("{:?}", 5u16.checked_add(65530u16));
    println!("{:?}", 6u16.checked_add(65530u16));
}

(playground)

Prints:

Some(65535)
None

Upvotes: 16

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