mirror of https://github.com/rust-lang/rust
69 lines
2.4 KiB
Rust
69 lines
2.4 KiB
Rust
//@ compile-flags: -Zmir-opt-level=0
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//@ error-pattern: cannot use f32::to_bits on a NaN
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#![feature(const_float_bits_conv)]
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#![feature(const_float_classify)]
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// Don't promote
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const fn nop<T>(x: T) -> T { x }
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macro_rules! const_assert {
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($a:expr) => {
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{
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const _: () = assert!($a);
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assert!(nop($a));
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}
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};
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($a:expr, $b:expr) => {
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{
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const _: () = assert!($a == $b);
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assert_eq!(nop($a), nop($b));
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}
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};
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}
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fn f32() {
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// Check that NaNs roundtrip their bits regardless of signalingness
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// 0xA is 0b1010; 0x5 is 0b0101 -- so these two together clobbers all the mantissa bits
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// ...actually, let's just check that these break. :D
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const MASKED_NAN1: u32 = f32::NAN.to_bits() ^ 0x002A_AAAA;
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//~^ inside
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const MASKED_NAN2: u32 = f32::NAN.to_bits() ^ 0x0055_5555;
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//~^ inside
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// The rest of the code is dead because the constants already fail to evaluate.
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const_assert!(f32::from_bits(MASKED_NAN1).is_nan());
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const_assert!(f32::from_bits(MASKED_NAN1).is_nan());
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// LLVM does not guarantee that loads and stores of NaNs preserve their exact bit pattern.
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// In practice, this seems to only cause a problem on x86, since the most widely used calling
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// convention mandates that floating point values are returned on the x87 FPU stack. See #73328.
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// However, during CTFE we still preserve bit patterns (though that is not a guarantee).
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const_assert!(f32::from_bits(MASKED_NAN1).to_bits(), MASKED_NAN1);
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const_assert!(f32::from_bits(MASKED_NAN2).to_bits(), MASKED_NAN2);
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}
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fn f64() {
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// Check that NaNs roundtrip their bits regardless of signalingness
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// 0xA is 0b1010; 0x5 is 0b0101 -- so these two together clobbers all the mantissa bits
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// ...actually, let's just check that these break. :D
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const MASKED_NAN1: u64 = f64::NAN.to_bits() ^ 0x000A_AAAA_AAAA_AAAA;
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//~^ inside
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const MASKED_NAN2: u64 = f64::NAN.to_bits() ^ 0x0005_5555_5555_5555;
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//~^ inside
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// The rest of the code is dead because the constants already fail to evaluate.
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const_assert!(f64::from_bits(MASKED_NAN1).is_nan());
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const_assert!(f64::from_bits(MASKED_NAN1).is_nan());
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// See comment above.
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const_assert!(f64::from_bits(MASKED_NAN1).to_bits(), MASKED_NAN1);
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const_assert!(f64::from_bits(MASKED_NAN2).to_bits(), MASKED_NAN2);
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}
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fn main() {
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f32();
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f64();
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}
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