use slice::align_to

src/libcore/slice/memchr.rs

@@ -102,32 +102,13 @@ pub fn memrchr(x: u8, text: &[u8]) -> Option<usize> {
  let ptr = text.as_ptr();
  let usize_bytes = mem::size_of::<usize>();
 
- // a version of align_offset that says how much must be *subtracted*
- // from a pointer to be aligned.
- #[inline(always)]
- fn align_offset_down(ptr: *const u8, align: usize) -> usize {
- let align_offset = ptr.align_offset(align);
- if align_offset > align {
- // Not possible to align
- usize::max_value()
- } else if align_offset == 0 {
- 0
- } else {
- // E.g. if align=8 and we have to add 1, then we can also subtract 7.
- align - align_offset
- }
- }
-
- // search to an aligned boundary
- let end_align = align_offset_down(unsafe { ptr.offset(len as isize) }, usize_bytes);
- let mut offset;
- if end_align > 0 {
- offset = if end_align >= len { 0 } else { len - end_align };
- if let Some(index) = text[offset..].iter().rposition(|elt| *elt == x) {
- return Some(offset + index);
- }
- } else {
- offset = len;
+ let mut offset = {
+ // We call this just to obtain the length of the suffix
+ let (_, _, suffix) = unsafe { text.align_to::<usize>() };
+ len - suffix.len()
+ };
+ if let Some(index) = text[offset..].iter().rposition(|elt| *elt == x) {
+ return Some(offset + index);
  }
 
  // search the body of the text