diff options
Diffstat (limited to 'library/alloc/src/vec/is_zero.rs')
| -rw-r--r-- | library/alloc/src/vec/is_zero.rs | 36 |
1 files changed, 32 insertions, 4 deletions
diff --git a/library/alloc/src/vec/is_zero.rs b/library/alloc/src/vec/is_zero.rs index edf270db81d..92a32779b8e 100644 --- a/library/alloc/src/vec/is_zero.rs +++ b/library/alloc/src/vec/is_zero.rs @@ -17,12 +17,14 @@ macro_rules! impl_is_zero { }; } +impl_is_zero!(i8, |x| x == 0); // It is needed to impl for arrays and tuples of i8. impl_is_zero!(i16, |x| x == 0); impl_is_zero!(i32, |x| x == 0); impl_is_zero!(i64, |x| x == 0); impl_is_zero!(i128, |x| x == 0); impl_is_zero!(isize, |x| x == 0); +impl_is_zero!(u8, |x| x == 0); // It is needed to impl for arrays and tuples of u8. impl_is_zero!(u16, |x| x == 0); impl_is_zero!(u32, |x| x == 0); impl_is_zero!(u64, |x| x == 0); @@ -54,15 +56,41 @@ unsafe impl<T: IsZero, const N: usize> IsZero for [T; N] { fn is_zero(&self) -> bool { // Because this is generated as a runtime check, it's not obvious that // it's worth doing if the array is really long. The threshold here - // is largely arbitrary, but was picked because as of 2022-05-01 LLVM - // can const-fold the check in `vec![[0; 32]; n]` but not in - // `vec![[0; 64]; n]`: https://godbolt.org/z/WTzjzfs5b + // is largely arbitrary, but was picked because as of 2022-07-01 LLVM + // fails to const-fold the check in `vec![[1; 32]; n]` + // See https://github.com/rust-lang/rust/pull/97581#issuecomment-1166628022 // Feel free to tweak if you have better evidence. - N <= 32 && self.iter().all(IsZero::is_zero) + N <= 16 && self.iter().all(IsZero::is_zero) } } +// This is recursive macro. +macro_rules! impl_for_tuples { + // Stopper + () => { + // No use for implementing for empty tuple because it is ZST. + }; + ($first_arg:ident $(,$rest:ident)*) => { + unsafe impl <$first_arg: IsZero, $($rest: IsZero,)*> IsZero for ($first_arg, $($rest,)*){ + #[inline] + fn is_zero(&self) -> bool{ + // Destructure tuple to N references + // Rust allows to hide generic params by local variable names. + #[allow(non_snake_case)] + let ($first_arg, $($rest,)*) = self; + + $first_arg.is_zero() + $( && $rest.is_zero() )* + } + } + + impl_for_tuples!($($rest),*); + } +} + +impl_for_tuples!(A, B, C, D, E, F, G, H); + // `Option<&T>` and `Option<Box<T>>` are guaranteed to represent `None` as null. // For fat pointers, the bytes that would be the pointer metadata in the `Some` // variant are padding in the `None` variant, so ignoring them and |