Does the shift of a negative undefined value change in Rust?

Question

Rust defines several operations with integers that give undefined behavior in C. The common theme is that they panic in debug mode and have a certain non-panic result in release mode. For example, copied integer panic overflows in debug mode, but end in release mode. There are also operator variants defined as wrapping_add() , saturating_add() , etc.

But what about offsetting a negative value? This behavior is undefined in C.

The following test example succeeds in Rust 1.17.0:

 #[test] fn negative_shift() { let i = -128i8; let j = i << 1; assert_eq!(j, 0); } 

Although he succeeds, he can still be undefined behavior ...

Answer 1

Rust Reference contains a list of all undefined behavior . The left offset of the sign number outside the size of this type is not in the list.