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Make sure we do not create an unaligned slice #42

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Merged
Veedrac merged 2 commits into from
Aug 3, 2018
Merged

Make sure we do not create an unaligned slice #42

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f25840a
Make sure we do not create an unaligned slice
RalfJung Aug 2, 2018
9fd343b
assert that the mid slice is aligned
RalfJung Aug 3, 2018
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7 changes: 6 additions & 1 deletion src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -178,12 +178,17 @@ fn chunk_align<Chunk: ByteChunk>(x: &[u8]) -> (&[u8], &[Chunk], &[u8]) {
let offset_ptr = (x.as_ptr() as usize) % align;
let offset_end = (x.as_ptr() as usize + x.len()) % align;

let d1 = (align - offset_ptr) % align; // `offset_ptr` might be 0, then `d1` should be 0.
let d2 = x.len().saturating_sub(offset_end);
let d1 = cmp::min((align - offset_ptr) % align, d2);
if d1 > d2 {
// No space for anything aligned
return (x, &[], &[]);
}

let (init, tail) = x.split_at(d2);
let (init, mid) = init.split_at(d1);
assert_eq!(mid.len() % align, 0);
assert_eq!(mid.as_ptr() as usize % mem::align_of::<Chunk>(), 0, "`mid` must be aligned");
let mid = unsafe { slice::from_raw_parts(mid.as_ptr() as *const Chunk, mid.len() / align) };

(init, mid, tail)
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