CODEWITHSUNDEEP
rust
Aaron H.
Aaron H.

Reputation: 6587

Is there a way to get a negative number with binary assignment without an overflowing_literals warning?

Is there a way to get a negative number with binary assignment without the warning while preserving the other, more valid warnings. Or am I thinking about this wrong?

const NEG: i32 = 0b1000_0000_0000_0000_0000_0000_0000_0000;
// -2147483648    

warning: literal out of range for i32
 --> src/main.rs:1:18
  |
1 | const NEG: i32 = 0b1000_0000_0000_0000_0000_0000_0000_0000;
  |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: #[warn(overflowing_literals)] on by default

Upvotes: 3

Views: 700

Answers (3)

Schwern
Schwern

Reputation: 164689

Or am I thinking about this wrong?

If all you want is the minimum and maximum i32, there's already MIN and MAX constants in the std::i32 module. They're easier to understand, and you can't make a mistake.

use std::i32;

fn main() {
    const POS: i32 = i32::MAX;
    const NEG: i32 = i32::MIN;
    println!("{} {}", NEG, POS);
}

Upvotes: 1

Shepmaster
Shepmaster

Reputation: 430574

You can start with an unsigned type and then cast to a signed:

const NEG: i32 = 0b1000_0000_0000_0000_0000_0000_0000_0000_u32 as i32;

without the warning while preserving the other, more valid warnings

You can disable specific warnings for specific expressions:

#[allow(overflowing_literals)]
const NEG: i32 = 0b1000_0000_0000_0000_0000_0000_0000_0000;

However, this original behavior seems incorrect. The binary value is not out of range of an i32. An issue seems to exist.

Upvotes: 6

Tim Diekmann
Tim Diekmann

Reputation: 8466

You can place a - in front of it:

// warning
const N1: i32 = 0b1000_0000_0000_0000_0000_0000_0000_0000;

// no warning
const N2: i32 = -0b1000_0000_0000_0000_0000_0000_0000_0000;

assert_eq!(N1, N2);

Playground

However, your case is a special case, since -N1 == N2. Otherwise you have to negate one result of course (otherwise it would be super unintuitive).

Upvotes: 1

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