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make memrchr use align_offset

This commit is contained in:
Ralf Jung 2018-07-26 18:29:38 +02:00
parent 0fc4501256
commit 70cb75c31e
1 changed files with 17 additions and 1 deletions
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18
src/libcore/slice/memchr.rs
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@ -102,8 +102,24 @@ 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 = (ptr as usize + len) & (usize_bytes - 1);
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 };