diff options
| -rw-r--r-- | library/core/src/ptr/mod.rs | 24 |
1 files changed, 11 insertions, 13 deletions
diff --git a/library/core/src/ptr/mod.rs b/library/core/src/ptr/mod.rs index 78308f97461..68b5d1df71c 100644 --- a/library/core/src/ptr/mod.rs +++ b/library/core/src/ptr/mod.rs @@ -1172,7 +1172,7 @@ pub(crate) unsafe fn align_offset<T: Sized>(p: *const T, a: usize) -> usize { /// Calculate multiplicative modular inverse of `x` modulo `m`. /// - /// This implementation is tailored for align_offset and has following preconditions: + /// This implementation is tailored for `align_offset` and has following preconditions: /// /// * `m` is a power-of-two; /// * `x < m`; (if `x ≥ m`, pass in `x % m` instead) @@ -1220,23 +1220,21 @@ pub(crate) unsafe fn align_offset<T: Sized>(p: *const T, a: usize) -> usize { } let stride = mem::size_of::<T>(); - // SAFETY: `a` is a power-of-two, hence non-zero. + // SAFETY: `a` is a power-of-two, therefore non-zero. let a_minus_one = unsafe { unchecked_sub(a, 1) }; - let pmoda = p as usize & a_minus_one; + if stride == 1 { + // `stride == 1` case can be computed more efficiently through `-p (mod a)`. + return wrapping_sub(0, p as usize) & a_minus_one; + } + let pmoda = p as usize & a_minus_one; if pmoda == 0 { // Already aligned. Yay! return 0; - } - - if stride <= 1 { - return if stride == 0 { - // If the pointer is not aligned, and the element is zero-sized, then no amount of - // elements will ever align the pointer. - !0 - } else { - wrapping_sub(a, pmoda) - }; + } else if stride == 0 { + // If the pointer is not aligned, and the element is zero-sized, then no amount of + // elements will ever align the pointer. + return usize::MAX; } let smoda = stride & a_minus_one; |