jhorstmann commented on a change in pull request #8571:
URL: https://github.com/apache/arrow/pull/8571#discussion_r518830136
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File path: rust/arrow/src/util/bit_chunk_iterator.rs
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@@ -55,48 +58,52 @@ impl<'a> BitChunks<'a> {
pub struct BitChunkIterator<'a> {
buffer: &'a Buffer,
raw_data: *const u8,
- offset: usize,
+ bit_offset: usize,
chunk_len: usize,
index: usize,
}
impl<'a> BitChunks<'a> {
+ /// Returns the number of remaining bits, guaranteed to be between 0 and
63 (inclusive)
#[inline]
pub const fn remainder_len(&self) -> usize {
self.remainder_len
}
+ /// Returns the bitmask of remaining bits
#[inline]
pub fn remainder_bits(&self) -> u64 {
let bit_len = self.remainder_len;
if bit_len == 0 {
0
} else {
- let byte_len = ceil(bit_len, 8);
Review comment:
Exactly. If we have 7 remainder bits for example, if the offset starts
at 0 it is enough to read `ceil(7, 8) = 1` byte, but if we start for example at
offset 4 we need to combine bits from `ceil(4+7, 8) = 2` bytes. The further
refactoring of the loop was then necessary because we may now need to combine
bits from 9 bytes, and the previous code (which only shifted after the loop)
would have overflowed an `u64`.
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