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use unions instead of transmute and add const safety comments

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This commit is contained in:
Trevor Spiteri 2020-02-26 11:59:37 +01:00
parent d15a98b878
commit 87f0dc63a8
1 changed files with 36 additions and 8 deletions
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44
src/libcore/num/mod.rs
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@ -2251,12 +2251,19 @@ assert_eq!(
```"),
#[stable(feature = "int_to_from_bytes", since = "1.32.0")]
#[rustc_const_stable(feature = "const_int_conversion", since = "1.43.0")]
#[allow_internal_unstable(const_transmute)]
// SAFETY: const sound because integers are plain old datatypes so we can always
// transmute them to arrays of bytes
#[allow_internal_unstable(const_fn_union)]
#[inline]
pub const fn to_ne_bytes(self) -> [u8; mem::size_of::<Self>()] {
#[repr(C)]
union Bytes {
val: $SelfT,
bytes: [u8; mem::size_of::<$SelfT>()],
}
// SAFETY: integers are plain old datatypes so we can always transmute them to
// arrays of bytes
unsafe { mem::transmute(self) }
unsafe { Bytes { val: self }.bytes }
}
}
@ -2362,11 +2369,18 @@ fn read_ne_", stringify!($SelfT), "(input: &mut &[u8]) -> ", stringify!($SelfT),
```"),
#[stable(feature = "int_to_from_bytes", since = "1.32.0")]
#[rustc_const_stable(feature = "const_int_conversion", since = "1.43.0")]
#[allow_internal_unstable(const_transmute)]
// SAFETY: const sound because integers are plain old datatypes so we can always
// transmute to them
#[allow_internal_unstable(const_fn_union)]
#[inline]
pub const fn from_ne_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
#[repr(C)]
union Bytes {
val: $SelfT,
bytes: [u8; mem::size_of::<$SelfT>()],
}
// SAFETY: integers are plain old datatypes so we can always transmute to them
unsafe { mem::transmute(bytes) }
unsafe { Bytes { bytes }.val }
}
}
}
@ -4190,12 +4204,19 @@ assert_eq!(
```"),
#[stable(feature = "int_to_from_bytes", since = "1.32.0")]
#[rustc_const_stable(feature = "const_int_conversion", since = "1.43.0")]
#[allow_internal_unstable(const_transmute)]
// SAFETY: const sound because integers are plain old datatypes so we can always
// transmute them to arrays of bytes
#[allow_internal_unstable(const_fn_union)]
#[inline]
pub const fn to_ne_bytes(self) -> [u8; mem::size_of::<Self>()] {
#[repr(C)]
union Bytes {
val: $SelfT,
bytes: [u8; mem::size_of::<$SelfT>()],
}
// SAFETY: integers are plain old datatypes so we can always transmute them to
// arrays of bytes
unsafe { mem::transmute(self) }
unsafe { Bytes { val: self }.bytes }
}
}
@ -4301,11 +4322,18 @@ fn read_ne_", stringify!($SelfT), "(input: &mut &[u8]) -> ", stringify!($SelfT),
```"),
#[stable(feature = "int_to_from_bytes", since = "1.32.0")]
#[rustc_const_stable(feature = "const_int_conversion", since = "1.43.0")]
#[allow_internal_unstable(const_transmute)]
// SAFETY: const sound because integers are plain old datatypes so we can always
// transmute to them
#[allow_internal_unstable(const_fn_union)]
#[inline]
pub const fn from_ne_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
#[repr(C)]
union Bytes {
val: $SelfT,
bytes: [u8; mem::size_of::<$SelfT>()],
}
// SAFETY: integers are plain old datatypes so we can always transmute to them
unsafe { mem::transmute(bytes) }
unsafe { Bytes { bytes }.val }
}
}
}