[GitHub] [arrow] jhorstmann commented on a change in pull request #8663: ARROW-10079: [Rust] Benchmark and improve count bits

[GitBox <gi...@apache.org>]

jhorstmann commented on a change in pull request #8663:
URL: https://github.com/apache/arrow/pull/8663#discussion_r523439893



##########
File path: rust/arrow/src/array/array_union.rs
##########
@@ -232,7 +231,7 @@ impl UnionArray {
         assert!(index - self.offset() < self.len());
         if self.is_dense() {
             let valid_slots = match self.data.null_buffer() {
-                Some(b) => bit_util::count_set_bits_offset(b.data(), 0, index),
+                Some(b) => b.count_set_bits_offset(0, index),

Review comment:
       Unrelated to this refactoring, but this code in `UnionArray` did not match my understanding of the [array format documentation][1]. At least I don't see any mention that the offsets array is compressed by omitting null values. Or maybe the documentation needs a better example that includes a null bitmap.
   
    [1]: https://arrow.apache.org/docs/format/Columnar.html#dense-union




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