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Vendor cfg_if::cfg_if!

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`cfg_if` is helpful for applying `cfg` attributes to groups of items,
like we will need to do with architecture-specific modules of `f16` and
`f128`. However, `libm` can't have dependencies.

The `cfg_if` macro is complex but small, so just vendor it here.
This commit is contained in:
Trevor Gross 2024-10-26 02:56:22 -05:00
parent ad1c652293
commit ec1ca51298
1 changed files with 43 additions and 3 deletions
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46
library/compiler-builtins/libm/src/math/support/macros.rs
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@ -1,6 +1,46 @@
/// Choose among using an intrinsic (if available) and falling back to the default function body.
/// Returns directly if the intrinsic version is used, otherwise continues to the rest of the
/// function.
/// `libm` cannot have dependencies, so this is vendored directly from the `cfg-if` crate
/// (with some comments stripped for compactness).
macro_rules! cfg_if {
// match if/else chains with a final `else`
($(
if #[cfg($meta:meta)] { $($tokens:tt)* }
) else * else {
$($tokens2:tt)*
}) => {
cfg_if! { @__items () ; $( ( ($meta) ($($tokens)*) ), )* ( () ($($tokens2)*) ), }
};
// match if/else chains lacking a final `else`
(
if #[cfg($i_met:meta)] { $($i_tokens:tt)* }
$( else if #[cfg($e_met:meta)] { $($e_tokens:tt)* } )*
) => {
cfg_if! {
@__items
() ;
( ($i_met) ($($i_tokens)*) ),
$( ( ($e_met) ($($e_tokens)*) ), )*
( () () ),
}
};
// Internal and recursive macro to emit all the items
//
// Collects all the negated cfgs in a list at the beginning and after the
// semicolon is all the remaining items
(@__items ($($not:meta,)*) ; ) => {};
(@__items ($($not:meta,)*) ; ( ($($m:meta),*) ($($tokens:tt)*) ), $($rest:tt)*) => {
#[cfg(all($($m,)* not(any($($not),*))))] cfg_if! { @__identity $($tokens)* }
cfg_if! { @__items ($($not,)* $($m,)*) ; $($rest)* }
};
// Internal macro to make __apply work out right for different match types,
// because of how macros matching/expand stuff.
(@__identity $($tokens:tt)*) => { $($tokens)* };
}
/// Choose between using an intrinsic (if available) and the function body. Returns directly if
/// the intrinsic is used, otherwise the rest of the function body is used.
///
/// Use this if the intrinsic is likely to be more performant on the platform(s) specified
/// in `intrinsic_available`.