i686 floating point behavior does not agree with unit tests in debug mode · Issue #73288 · rust-lang/rust (original) (raw)

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@ecstatic-morse

Description

@ecstatic-morse

Compiling and running the following code with -C opt-level=0 for 32-bit Linux on a recent nightly (2020-06-07) results in a failing assertion.

fn main() { let masked_nan2 = f32::NAN.to_bits() ^ 0x0055_5555; assert_eq!(f32::from_bits(masked_nan2).to_bits(), masked_nan2); }

rustc +nightly --target=i686-unknown-linux-gnu test.rs && ./test

Output:

thread 'main' panicked at 'assertion failed: `(left == right)`
  left: `2144687445`,
 right: `2140493141`', test.rs:3:5

However, this code is taken directly from a unit test for libstd added in #46012, so presumably it should succeed.

let masked_nan1 = f32::NAN.to_bits() ^ 0x002A_AAAA;
let masked_nan2 = f32::NAN.to_bits() ^ 0x0055_5555;
assert!(f32::from_bits(masked_nan1).is_nan());
assert!(f32::from_bits(masked_nan2).is_nan());
assert_eq!(f32::from_bits(masked_nan1).to_bits(), masked_nan1);
assert_eq!(f32::from_bits(masked_nan2).to_bits(), masked_nan2);