diff options
| -rw-r--r-- | drivers/gpu/nova-core/num.rs | 52 |
1 files changed, 52 insertions, 0 deletions
diff --git a/drivers/gpu/nova-core/num.rs b/drivers/gpu/nova-core/num.rs index 92a91b9e30de..c952a834e662 100644 --- a/drivers/gpu/nova-core/num.rs +++ b/drivers/gpu/nova-core/num.rs @@ -163,3 +163,55 @@ where T::from_safe_cast(self) } } + +/// Implements lossless conversion of a constant from a larger type into a smaller one. +macro_rules! impl_const_into { + ($from:ty => { $($into:ty),* }) => { + $( + paste! { + #[doc = ::core::concat!( + "Performs a build-time safe conversion of a [`", + ::core::stringify!($from), + "`] constant value into a [`", + ::core::stringify!($into), + "`].")] + /// + /// This checks at compile-time that the conversion is lossless, and triggers a build + /// error if it isn't. + /// + /// # Examples + /// + /// ``` + /// use crate::num; + /// + /// // Succeeds because the value of the source fits into the destination's type. + #[doc = ::core::concat!( + "assert_eq!(num::", + ::core::stringify!($from), + "_into_", + ::core::stringify!($into), + "::<1", + ::core::stringify!($from), + ">(), 1", + ::core::stringify!($into), + ");")] + /// ``` + #[allow(unused)] + pub(crate) const fn [<$from _into_ $into>]<const N: $from>() -> $into { + // Make sure that the target type is smaller than the source one. + static_assert!($from::BITS >= $into::BITS); + // CAST: we statically enforced above that `$from` is larger than `$into`, so the + // `as` conversion will be lossless. + build_assert!(N >= $into::MIN as $from && N <= $into::MAX as $from); + + N as $into + } + } + )* + }; +} + +impl_const_into!(usize => { u8, u16, u32 }); +impl_const_into!(u64 => { u8, u16, u32 }); +impl_const_into!(u32 => { u8, u16 }); +impl_const_into!(u16 => { u8 }); |