mbutrovich commented on code in PR #10136:
URL: https://github.com/apache/arrow-rs/pull/10136#discussion_r4094211181
##########
arrow-buffer/src/util/bit_chunk_iterator.rs:
##########
@@ -360,6 +374,38 @@ impl<'a> IntoIterator for &BitChunks<'a> {
}
}
+/// Reads the `index`th complete 64-bit chunk of `buffer`, whose bits start
+/// at `bit_offset` (in `0..8`)
+///
+/// # Safety
+///
+/// `index` must be less than the number of complete chunks, so that the
+/// buffer holds at least `index * 8 + 8` bytes, plus one more byte when
+/// `bit_offset != 0` (the remainder byte the constructor guarantees)
+#[inline]
+unsafe fn read_chunk(buffer: &[u8], bit_offset: usize, index: usize) -> u64 {
+ // cast to *const u64 should be fine since we are using read_unaligned
below
Review Comment:
`bit_offset` can be 0 here, and `read_chunk` is a free function without
`chunk_len`, so those two asserts would need adjusting. Checking the byte count
from the `# Safety` doc directly would work for both callers:
```rust
debug_assert!(bit_offset < 8);
debug_assert!(buffer.len() >= index * 8 + 8 + usize::from(bit_offset !=
0));
```
I ran the `arrow-buffer` `bit_chunk` tests and the `arrow-select` filter
tests with these in place and they pass.
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