bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

Auto merge of #96946 - WaffleLapkin:ptr_mask, r=scottmcm

Browse source 
Add pointer masking convenience functions

This PR adds the following public API:
```rust
impl<T: ?Sized> *const T {
    fn mask(self, mask: usize) -> *const T;
}

impl<T: ?Sized> *mut T {
    fn mask(self, mask: usize) -> *const T;
}

// mod intrinsics
fn mask<T>(ptr: *const T, mask: usize) -> *const T
```
This is equivalent to `ptr.map_addr(|a| a & mask)` but also uses a cool llvm intrinsic.

Proposed in https://github.com/rust-lang/rust/pull/95643#issuecomment-1121562352

cc `@Gankra` `@scottmcm` `@RalfJung`

r? rust-lang/libs-api
This commit is contained in:
bors 2022-08-28 01:34:47 +00:00
commit 1e978a3627
10 changed files with 87 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

15
library/core/src/ptr/mut_ptr.rs
View file

@ -575,6 +575,21 @@ impl<T: ?Sized> *mut T {
)
}
/// Masks out bits of the pointer according to a mask.
///
/// This is convenience for `ptr.map_addr(|a| a & mask)`.
///
/// For non-`Sized` pointees this operation changes only the data pointer,
/// leaving the metadata untouched.
#[cfg(not(bootstrap))]
#[unstable(feature = "ptr_mask", issue = "98290")]
#[must_use = "returns a new pointer rather than modifying its argument"]
#[inline(always)]
pub fn mask(self, mask: usize) -> *mut T {
let this = intrinsics::ptr_mask(self.cast::<()>(), mask) as *mut ();
from_raw_parts_mut::<T>(this, metadata(self))
}
/// Returns `None` if the pointer is null, or else returns a unique reference to
/// the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_mut`]
/// must be used instead.