alamb commented on code in PR #26507:
URL: https://github.com/apache/datafusion/pull/26507#discussion_r4417832570
##########
datafusion/common/src/utils/mod.rs:
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@@ -1266,6 +1266,94 @@ pub fn offset_span<O: ArrowNativeType>(offsets:
&OffsetBuffer<O>) -> (usize, usi
(start, offsets.last().as_usize() - start)
}
+/// Counts the set bits that precede a sequence of non-decreasing positions in
a
+/// bitmap, reading each 64-bit word of the bitmap once.
+///
+/// This suits a single pass over the rows of a list, where each call costs a
+/// mask and a popcount when the position is in the current word. `words`
yields
+/// the bitmap's 64-bit words, starting with its first bit, such as
+/// [`BooleanBuffer::bit_chunks`] with [`BitChunks::iter_padded`].
+///
+/// [`BooleanBuffer::bit_chunks`]: arrow::buffer::BooleanBuffer::bit_chunks
+/// [`BitChunks::iter_padded`]:
arrow::util::bit_chunk_iterator::BitChunks::iter_padded
+///
+/// ```
+/// # use arrow::buffer::BooleanBuffer;
+/// # use datafusion_common::utils::SetBitCounter;
+/// let bits = BooleanBuffer::from(vec![true, false, true, true, false]);
+/// let mut counter = SetBitCounter::new(bits.bit_chunks().iter_padded());
+/// assert_eq!(counter.count_before(1), 1);
+/// assert_eq!(counter.count_range(1, 5), 2);
+/// ```
+pub struct SetBitCounter<I> {
Review Comment:
I agree an upstream issue would be good
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