Add is_aligned{,_to} convenience methods to NonNull

Author: WaffleLapkin

library/core/src/ptr/non_null.rs

@@ -1282,6 +1282,240 @@ impl<T: ?Sized> NonNull<T> {
             unsafe { ptr::align_offset(self.pointer, align) }
         }
     }
+
+    /// Returns whether the pointer is properly aligned for `T`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(pointer_is_aligned)]
+    /// use std::ptr::NonNull;
+    ///
+    /// // On some platforms, the alignment of i32 is less than 4.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    ///
+    /// let data = AlignedI32(42);
+    /// let ptr = NonNull::<AlignedI32>::from(&data);
+    ///
+    /// assert!(ptr.is_aligned());
+    /// assert!(!NonNull::new(ptr.as_ptr().wrapping_byte_add(1)).unwrap().is_aligned());
+    /// ```
+    ///
+    /// # At compiletime
+    /// **Note: Alignment at compiletime is experimental and subject to change. See the
+    /// [tracking issue] for details.**
+    ///
+    /// At compiletime, the compiler may not know where a value will end up in memory.
+    /// Calling this function on a pointer created from a reference at compiletime will only
+    /// return `true` if the pointer is guaranteed to be aligned. This means that the pointer
+    /// is never aligned if cast to a type with a stricter alignment than the reference's
+    /// underlying allocation.
+    ///
+    /// ```
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(const_pointer_is_aligned)]
+    /// #![feature(non_null_convenience)]
+    /// #![feature(const_option)]
+    /// #![feature(const_nonnull_new)]
+    /// use std::ptr::NonNull;
+    ///
+    /// // On some platforms, the alignment of primitives is less than their size.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    /// #[repr(align(8))]
+    /// struct AlignedI64(i64);
+    ///
+    /// const _: () = {
+    ///     let data = [AlignedI32(42), AlignedI32(42)];
+    ///     let ptr = NonNull::<AlignedI32>::new(&data[0] as *const _ as *mut _).unwrap();
+    ///     assert!(ptr.is_aligned());
+    ///
+    ///     // At runtime either `ptr1` or `ptr2` would be aligned, but at compiletime neither is aligned.
+    ///     let ptr1 = ptr.cast::<AlignedI64>();
+    ///     let ptr2 = unsafe { ptr.add(1).cast::<AlignedI64>() };
+    ///     assert!(!ptr1.is_aligned());
+    ///     assert!(!ptr2.is_aligned());
+    /// };
+    /// ```
+    ///
+    /// Due to this behavior, it is possible that a runtime pointer derived from a compiletime
+    /// pointer is aligned, even if the compiletime pointer wasn't aligned.
+    ///
+    /// ```
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(const_pointer_is_aligned)]
+    ///
+    /// // On some platforms, the alignment of primitives is less than their size.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    /// #[repr(align(8))]
+    /// struct AlignedI64(i64);
+    ///
+    /// // At compiletime, neither `COMPTIME_PTR` nor `COMPTIME_PTR + 1` is aligned.
+    /// const COMPTIME_PTR: *const AlignedI32 = &AlignedI32(42);
+    /// const _: () = assert!(!COMPTIME_PTR.cast::<AlignedI64>().is_aligned());
+    /// const _: () = assert!(!COMPTIME_PTR.wrapping_add(1).cast::<AlignedI64>().is_aligned());
+    ///
+    /// // At runtime, either `runtime_ptr` or `runtime_ptr + 1` is aligned.
+    /// let runtime_ptr = COMPTIME_PTR;
+    /// assert_ne!(
+    ///     runtime_ptr.cast::<AlignedI64>().is_aligned(),
+    ///     runtime_ptr.wrapping_add(1).cast::<AlignedI64>().is_aligned(),
+    /// );
+    /// ```
+    ///
+    /// If a pointer is created from a fixed address, this function behaves the same during
+    /// runtime and compiletime.
+    ///
+    /// ```
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(const_pointer_is_aligned)]
+    /// #![feature(const_option)]
+    /// #![feature(const_nonnull_new)]
+    /// use std::ptr::NonNull;
+    ///
+    /// // On some platforms, the alignment of primitives is less than their size.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    /// #[repr(align(8))]
+    /// struct AlignedI64(i64);
+    ///
+    /// const _: () = {
+    ///     let ptr = NonNull::new(40 as *mut AlignedI32).unwrap();
+    ///     assert!(ptr.is_aligned());
+    ///
+    ///     // For pointers with a known address, runtime and compiletime behavior are identical.
+    ///     let ptr1 = ptr.cast::<AlignedI64>();
+    ///     let ptr2 = NonNull::new(ptr.as_ptr().wrapping_add(1)).unwrap().cast::<AlignedI64>();
+    ///     assert!(ptr1.is_aligned());
+    ///     assert!(!ptr2.is_aligned());
+    /// };
+    /// ```
+    ///
+    /// [tracking issue]: https://github.com/rust-lang/rust/issues/104203
+    #[unstable(feature = "pointer_is_aligned", issue = "96284")]
+    #[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "104203")]
+    #[must_use]
+    #[inline]
+    pub const fn is_aligned(self) -> bool
+    where
+        T: Sized,
+    {
+        self.pointer.is_aligned()
+    }
+
+    /// Returns whether the pointer is aligned to `align`.
+    ///
+    /// For non-`Sized` pointees this operation considers only the data pointer,
+    /// ignoring the metadata.
+    ///
+    /// # Panics
+    ///
+    /// The function panics if `align` is not a power-of-two (this includes 0).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(pointer_is_aligned)]
+    ///
+    /// // On some platforms, the alignment of i32 is less than 4.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    ///
+    /// let data = AlignedI32(42);
+    /// let ptr = &data as *const AlignedI32;
+    ///
+    /// assert!(ptr.is_aligned_to(1));
+    /// assert!(ptr.is_aligned_to(2));
+    /// assert!(ptr.is_aligned_to(4));
+    ///
+    /// assert!(ptr.wrapping_byte_add(2).is_aligned_to(2));
+    /// assert!(!ptr.wrapping_byte_add(2).is_aligned_to(4));
+    ///
+    /// assert_ne!(ptr.is_aligned_to(8), ptr.wrapping_add(1).is_aligned_to(8));
+    /// ```
+    ///
+    /// # At compiletime
+    /// **Note: Alignment at compiletime is experimental and subject to change. See the
+    /// [tracking issue] for details.**
+    ///
+    /// At compiletime, the compiler may not know where a value will end up in memory.
+    /// Calling this function on a pointer created from a reference at compiletime will only
+    /// return `true` if the pointer is guaranteed to be aligned. This means that the pointer
+    /// cannot be stricter aligned than the reference's underlying allocation.
+    ///
+    /// ```
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(const_pointer_is_aligned)]
+    ///
+    /// // On some platforms, the alignment of i32 is less than 4.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    ///
+    /// const _: () = {
+    ///     let data = AlignedI32(42);
+    ///     let ptr = &data as *const AlignedI32;
+    ///
+    ///     assert!(ptr.is_aligned_to(1));
+    ///     assert!(ptr.is_aligned_to(2));
+    ///     assert!(ptr.is_aligned_to(4));
+    ///
+    ///     // At compiletime, we know for sure that the pointer isn't aligned to 8.
+    ///     assert!(!ptr.is_aligned_to(8));
+    ///     assert!(!ptr.wrapping_add(1).is_aligned_to(8));
+    /// };
+    /// ```
+    ///
+    /// Due to this behavior, it is possible that a runtime pointer derived from a compiletime
+    /// pointer is aligned, even if the compiletime pointer wasn't aligned.
+    ///
+    /// ```
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(const_pointer_is_aligned)]
+    ///
+    /// // On some platforms, the alignment of i32 is less than 4.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    ///
+    /// // At compiletime, neither `COMPTIME_PTR` nor `COMPTIME_PTR + 1` is aligned.
+    /// const COMPTIME_PTR: *const AlignedI32 = &AlignedI32(42);
+    /// const _: () = assert!(!COMPTIME_PTR.is_aligned_to(8));
+    /// const _: () = assert!(!COMPTIME_PTR.wrapping_add(1).is_aligned_to(8));
+    ///
+    /// // At runtime, either `runtime_ptr` or `runtime_ptr + 1` is aligned.
+    /// let runtime_ptr = COMPTIME_PTR;
+    /// assert_ne!(
+    ///     runtime_ptr.is_aligned_to(8),
+    ///     runtime_ptr.wrapping_add(1).is_aligned_to(8),
+    /// );
+    /// ```
+    ///
+    /// If a pointer is created from a fixed address, this function behaves the same during
+    /// runtime and compiletime.
+    ///
+    /// ```
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(const_pointer_is_aligned)]
+    ///
+    /// const _: () = {
+    ///     let ptr = 40 as *const u8;
+    ///     assert!(ptr.is_aligned_to(1));
+    ///     assert!(ptr.is_aligned_to(2));
+    ///     assert!(ptr.is_aligned_to(4));
+    ///     assert!(ptr.is_aligned_to(8));
+    ///     assert!(!ptr.is_aligned_to(16));
+    /// };
+    /// ```
+    ///
+    /// [tracking issue]: https://github.com/rust-lang/rust/issues/104203
+    #[unstable(feature = "pointer_is_aligned", issue = "96284")]
+    #[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "104203")]
+    #[must_use]
+    #[inline]
+    pub const fn is_aligned_to(self, align: usize) -> bool {
+        self.pointer.is_aligned_to(align)
+    }
 }
 
 impl<T> NonNull<[T]> {