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Use transmute_copy where appropriate. Format some docs.

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This commit is contained in:
Lokathor 2020-08-18 17:02:06 -06:00
parent d2e161bddd
commit 6414f14815
1 changed files with 12 additions and 20 deletions
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32
src/lib.rs
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@ -223,20 +223,13 @@ impl std::error::Error for PodCastError {}
///
/// ## Panics
///
/// This is [`try_cast`] but will panic on error.
/// * This is like [`try_cast`](try_cast), but will panic on a size mismatch.
#[inline]
pub fn cast<A: Pod, B: Pod>(a: A) -> B {
if size_of::<A>() == size_of::<B>() {
// Plz mr compiler, just notice that we can't ever hit Err in this case.
match try_cast(a) {
Ok(b) => b,
Err(_) => unreachable!(),
}
unsafe { core::mem::transmute_copy(&a) }
} else {
match try_cast(a) {
Ok(b) => b,
Err(e) => something_went_wrong("cast", e),
}
something_went_wrong("cast", PodCastError::SizeMismatch)
}
}
@ -324,19 +317,18 @@ pub fn pod_align_to_mut<T: Pod, U: Pod>(
/// Try to cast `T` into `U`.
///
/// Note that for this particular type of cast, alignment isn't a factor. The
/// input value is semantically copied into the function and then returned to a
/// new memory location which will have whatever the required alignment of the
/// output type is.
///
/// ## Failure
///
/// * If the types don't have the same size this fails.
#[inline]
pub fn try_cast<A: Pod, B: Pod>(a: A) -> Result<B, PodCastError> {
if size_of::<A>() == size_of::<B>() {
let mut b = B::zeroed();
// Note(Lokathor): We copy in terms of `u8` because that allows us to bypass
// any potential alignment difficulties.
let ap = &a as *const A as *const u8;
let bp = &mut b as *mut B as *mut u8;
unsafe { ap.copy_to_nonoverlapping(bp, size_of::<A>()) };
Ok(b)
Ok(unsafe { core::mem::transmute_copy(&a) })
} else {
Err(PodCastError::SizeMismatch)
}
@ -394,8 +386,7 @@ pub fn try_cast_mut<A: Pod, B: Pod>(a: &mut A) -> Result<&mut B, PodCastError> {
/// type, and the output slice wouldn't be a whole number of elements when
/// accounting for the size change (eg: 3 `u16` values is 1.5 `u32` values, so
/// that's a failure).
/// * Similarly, you can't convert between a
/// [ZST](https://doc.rust-lang.org/nomicon/exotic-sizes.html#zero-sized-types-zsts)
/// * Similarly, you can't convert between a [ZST](https://doc.rust-lang.org/nomicon/exotic-sizes.html#zero-sized-types-zsts)
/// and a non-ZST.
#[inline]
pub fn try_cast_slice<A: Pod, B: Pod>(a: &[A]) -> Result<&[B], PodCastError> {
@ -417,7 +408,8 @@ pub fn try_cast_slice<A: Pod, B: Pod>(a: &[A]) -> Result<&[B], PodCastError> {
}
}
/// Try to convert `&mut [T]` into `&mut [U]` (possibly with a change in length).
/// Try to convert `&mut [T]` into `&mut [U]` (possibly with a change in
/// length).
///
/// As [`try_cast_slice`], but `&mut`.
#[inline]