Manishearth commented on code in PR #6551:
URL: https://github.com/apache/arrow-rs/pull/6551#discussion_r1799749413
##########
arrow-buffer/src/util/bit_mask.rs:
##########
@@ -127,16 +127,16 @@ unsafe fn set_upto_64bits(
}
/// # Safety
-/// The caller must ensure all arguments are within the valid range.
+/// The caller must ensure `data` has `offset..(offset + 8)` range
#[inline]
unsafe fn read_bytes_to_u64(data: &[u8], offset: usize, count: usize) -> u64 {
debug_assert!(count <= 8);
- let mut tmp = std::mem::MaybeUninit::<u64>::new(0);
+ let mut tmp : u64 = 0;
let src = data.as_ptr().add(offset);
unsafe {
- std::ptr::copy_nonoverlapping(src, tmp.as_mut_ptr() as *mut u8, count);
- tmp.assume_init()
+ std::ptr::copy_nonoverlapping(src, &mut tmp as *mut _ as *mut u8,
count);
Review Comment:
Yes, either the debug assertion should be a real assertion or we should
clamp.
##########
arrow-buffer/src/util/bit_mask.rs:
##########
@@ -127,16 +127,16 @@ unsafe fn set_upto_64bits(
}
/// # Safety
-/// The caller must ensure all arguments are within the valid range.
+/// The caller must ensure `data` has `offset..(offset + 8)` range
#[inline]
unsafe fn read_bytes_to_u64(data: &[u8], offset: usize, count: usize) -> u64 {
debug_assert!(count <= 8);
- let mut tmp = std::mem::MaybeUninit::<u64>::new(0);
+ let mut tmp : u64 = 0;
let src = data.as_ptr().add(offset);
unsafe {
- std::ptr::copy_nonoverlapping(src, tmp.as_mut_ptr() as *mut u8, count);
- tmp.assume_init()
+ std::ptr::copy_nonoverlapping(src, &mut tmp as *mut _ as *mut u8,
count);
Review Comment:
_or_ the function should be documented with clearer invariants. It is an
unsafe function after all, it's allowed to assume these things, but "all
arguments are within range" is two separate checks: that count is not more than
8, and that offset/count is in range. The next commit adds the latter, not the
former.
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