diff options
Diffstat (limited to 'src/libcore/ptr.rs')
| -rw-r--r-- | src/libcore/ptr.rs | 75 |
1 files changed, 74 insertions, 1 deletions
diff --git a/src/libcore/ptr.rs b/src/libcore/ptr.rs index dd01534ec02..4041a3760e5 100644 --- a/src/libcore/ptr.rs +++ b/src/libcore/ptr.rs @@ -1064,7 +1064,43 @@ impl<T: ?Sized> *const T { copy_nonoverlapping(self, dest, count) } - + /// Computes the byte offset that needs to be applied in order to + /// make the pointer aligned to `align`. + /// If it is not possible to align the pointer, the implementation returns + /// `usize::max_value()`. + /// + /// There are no guarantees whatsover that offsetting the pointer will not + /// overflow or go beyond the allocation that the pointer points into. + /// It is up to the caller to ensure that the returned offset is correct + /// in all terms other than alignment. + /// + /// # Examples + /// + /// Accessing adjacent `u8` as `u16` + /// + /// ``` + /// # #![feature(align_offset)] + /// # fn foo(n: usize) { + /// # use std::mem::align_of; + /// # unsafe { + /// let x = [5u8, 6u8, 7u8, 8u8, 9u8]; + /// let ptr = &x[n] as *const u8; + /// let offset = ptr.align_offset(align_of::<u16>()); + /// if offset < x.len() - n - 1 { + /// let u16_ptr = ptr.offset(offset as isize) as *const u16; + /// assert_ne!(*u16_ptr, 500); + /// } else { + /// // while the pointer can be aligned via `offset`, it would point + /// // outside the allocation + /// } + /// # } } + /// ``` + #[unstable(feature = "align_offset", issue = "44488")] + pub fn align_offset(self, align: usize) -> usize { + unsafe { + intrinsics::align_offset(self as *const _, align) + } + } } #[lang = "mut_ptr"] @@ -1284,6 +1320,43 @@ impl<T: ?Sized> *mut T { } } + /// Computes the byte offset that needs to be applied in order to + /// make the pointer aligned to `align`. + /// If it is not possible to align the pointer, the implementation returns + /// `usize::max_value()`. + /// + /// There are no guarantees whatsover that offsetting the pointer will not + /// overflow or go beyond the allocation that the pointer points into. + /// It is up to the caller to ensure that the returned offset is correct + /// in all terms other than alignment. + /// + /// # Examples + /// + /// Accessing adjacent `u8` as `u16` + /// + /// ``` + /// # #![feature(align_offset)] + /// # fn foo(n: usize) { + /// # use std::mem::align_of; + /// # unsafe { + /// let x = [5u8, 6u8, 7u8, 8u8, 9u8]; + /// let ptr = &x[n] as *const u8; + /// let offset = ptr.align_offset(align_of::<u16>()); + /// if offset < x.len() - n - 1 { + /// let u16_ptr = ptr.offset(offset as isize) as *const u16; + /// assert_ne!(*u16_ptr, 500); + /// } else { + /// // while the pointer can be aligned via `offset`, it would point + /// // outside the allocation + /// } + /// # } } + /// ``` + #[unstable(feature = "align_offset", issue = "44488")] + pub fn align_offset(self, align: usize) -> usize { + unsafe { + intrinsics::align_offset(self as *const _, align) + } + } /// Calculates the offset from a pointer (convenience for `.offset(count as isize)`). /// |