diff options
Diffstat (limited to 'src/libstd')
| -rw-r--r-- | src/libstd/f32.rs | 24 | ||||
| -rw-r--r-- | src/libstd/f64.rs | 13 |
2 files changed, 24 insertions, 13 deletions
diff --git a/src/libstd/f32.rs b/src/libstd/f32.rs index 7d79fb07811..a6eb17c8fa4 100644 --- a/src/libstd/f32.rs +++ b/src/libstd/f32.rs @@ -1131,13 +1131,16 @@ impl f32 { #[inline] pub fn from_bits(mut v: u32) -> Self { const EXP_MASK: u32 = 0x7F800000; - const QNAN_MASK: u32 = 0x00400000; const FRACT_MASK: u32 = 0x007FFFFF; if v & EXP_MASK == EXP_MASK && v & FRACT_MASK != 0 { - // If we have a NaN value, we - // convert signaling NaN values to quiet NaN - // by setting the the highest bit of the fraction - v |= QNAN_MASK; + // While IEEE 754-2008 specifies encodings for quiet NaNs + // and signaling ones, certain MIPS and PA-RISC + // CPUs treat signaling NaNs differently. + // Therefore to be safe, we pass a known quiet NaN + // if v is any kind of NaN. + // The check above only assumes IEEE 754-1985 to be + // valid. + v = unsafe { ::mem::transmute(NAN) }; } unsafe { ::mem::transmute(v) } } @@ -1732,8 +1735,15 @@ mod tests { } #[test] fn test_snan_masking() { + // NOTE: this test assumes that our current platform + // implements IEEE 754-2008 that specifies the difference + // in encoding of quiet and signaling NaNs. + // If you are porting Rust to a platform that does not + // implement IEEE 754-2008 (but e.g. IEEE 754-1985, which + // only says that "Signaling NaNs shall be reserved operands" + // but doesn't specify the actual setup), feel free to + // cfg out this test. let snan: u32 = 0x7F801337; - const PAYLOAD_MASK: u32 = 0x003FFFFF; const QNAN_MASK: u32 = 0x00400000; let nan_masked_fl = f32::from_bits(snan); let nan_masked = nan_masked_fl.to_bits(); @@ -1742,7 +1752,5 @@ mod tests { // Ensure that we have a quiet NaN assert_ne!(nan_masked & QNAN_MASK, 0); assert!(nan_masked_fl.is_nan()); - // Ensure the payload wasn't touched during conversion - assert_eq!(nan_masked & PAYLOAD_MASK, snan & PAYLOAD_MASK); } } diff --git a/src/libstd/f64.rs b/src/libstd/f64.rs index d5b0cd3a1fc..4d8d8b4ebe6 100644 --- a/src/libstd/f64.rs +++ b/src/libstd/f64.rs @@ -1046,13 +1046,16 @@ impl f64 { #[inline] pub fn from_bits(mut v: u64) -> Self { const EXP_MASK: u64 = 0x7FF0000000000000; - const QNAN_MASK: u64 = 0x0001000000000000; const FRACT_MASK: u64 = 0x000FFFFFFFFFFFFF; if v & EXP_MASK == EXP_MASK && v & FRACT_MASK != 0 { - // If we have a NaN value, we - // convert signaling NaN values to quiet NaN - // by setting the the highest bit of the fraction - v |= QNAN_MASK; + // While IEEE 754-2008 specifies encodings for quiet NaNs + // and signaling ones, certain MIPS and PA-RISC + // CPUs treat signaling NaNs differently. + // Therefore to be safe, we pass a known quiet NaN + // if v is any kind of NaN. + // The check above only assumes IEEE 754-1985 to be + // valid. + v = unsafe { ::mem::transmute(NAN) }; } unsafe { ::mem::transmute(v) } } |