diff --git a/compiler/rustc_apfloat/src/ieee.rs b/compiler/rustc_apfloat/src/ieee.rs index e3d941cad7a..aafd6dfb89a 100644 --- a/compiler/rustc_apfloat/src/ieee.rs +++ b/compiler/rustc_apfloat/src/ieee.rs @@ -1511,6 +1511,18 @@ impl FloatConvert> for IeeeFloat { sig::set_bit(&mut r.sig, T::PRECISION - 1); } + // If we are truncating NaN, it is possible that we shifted out all of the + // set bits in a signalling NaN payload. But NaN must remain NaN, so some + // bit in the significand must be set (otherwise it is Inf). + // This can only happen with sNaN. Set the 1st bit after the quiet bit, + // so that we still have an sNaN. + if r.sig[0] == 0 { + assert!(shift < 0, "Should not lose NaN payload on extend"); + assert!(T::PRECISION >= 3, "Unexpectedly narrow significand"); + assert!(*loses_info, "Missing payload should have set lost info"); + sig::set_bit(&mut r.sig, T::PRECISION - 3); + } + // gcc forces the Quiet bit on, which means (float)(double)(float_sNan) // does not give you back the same bits. This is dubious, and we // don't currently do it. You're really supposed to get diff --git a/compiler/rustc_apfloat/tests/ieee.rs b/compiler/rustc_apfloat/tests/ieee.rs index 2d8bb7d1e8e..0f3c99fba9e 100644 --- a/compiler/rustc_apfloat/tests/ieee.rs +++ b/compiler/rustc_apfloat/tests/ieee.rs @@ -566,6 +566,15 @@ fn fma() { } } +#[test] +fn issue_69532() { + let f = Double::from_bits(0x7FF0_0000_0000_0001u64 as u128); + let mut loses_info = false; + let r: Single = f.convert(&mut loses_info).value; + assert!(loses_info); + assert!(r.is_nan()); +} + #[test] fn min_num() { let f1 = Double::from_f64(1.0); diff --git a/src/test/ui/issues/issue-69532.rs b/src/test/ui/issues/issue-69532.rs new file mode 100644 index 00000000000..81007b15074 --- /dev/null +++ b/src/test/ui/issues/issue-69532.rs @@ -0,0 +1,24 @@ +// run-pass +#![feature(const_fn_transmute)] + +const fn make_nans() -> (f64, f64, f32, f32) { + let nan1: f64 = unsafe { std::mem::transmute(0x7FF0_0001_0000_0001u64) }; + let nan2: f64 = unsafe { std::mem::transmute(0x7FF0_0000_0000_0001u64) }; + + let nan1_32 = nan1 as f32; + let nan2_32 = nan2 as f32; + + (nan1, nan2, nan1_32, nan2_32) +} + +static NANS: (f64, f64, f32, f32) = make_nans(); + +fn main() { + let (nan1, nan2, nan1_32, nan2_32) = NANS; + + assert!(nan1.is_nan()); + assert!(nan2.is_nan()); + + assert!(nan1_32.is_nan()); + assert!(nan2_32.is_nan()); +}