This is, once again, an ARM-specific bug.

When this code is compiled with LLVM(or release GCC on x86_64, or debug GCC on ARM), it prints NaN.

When the same code is compiled with release GCC on ARM, it produces an infinity value instead.

#[no_mangle] #[inline(never)] fn dump_var(val3: f32) { println!("{val3:?}") } fn fn2(param: f32) { let inf = param * 170141170000000000000000000000000000000.0; let should_be_nan = inf + 0.0 - inf; dump_var(should_be_nan); } fn main() { fn2(3.0); }

Subtracting infinity from ininifty ought to result in an NaN value.