[GitHub] [arrow-rs] jhorstmann commented on a diff in pull request #3062: Fix null_count computation in binary

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

jhorstmann commented on code in PR #3062:
URL: https://github.com/apache/arrow-rs/pull/3062#discussion_r1017668466


##########
arrow/src/compute/kernels/arithmetic.rs:
##########
@@ -3044,4 +3044,61 @@ mod tests {
         let c = add(&a, &b).unwrap();
         assert_eq!(c, expected);
     }
+
+    #[test]
+    fn test_resize_builder() {
+        let mut null_buffer_builder = BooleanBufferBuilder::new(16);
+        null_buffer_builder.append_slice(&[
+            false, false, false, false, false, false, false, false, false, false, false,
+            false, false, true, true, true,
+        ]);
+        // `resize` resizes the buffer length to the ceil of byte numbers.
+        // So the underlying buffer is not changed.
+        null_buffer_builder.resize(13);
+        assert_eq!(null_buffer_builder.len(), 13);
+
+        let null_buffer = null_buffer_builder.finish();
+
+        // `count_set_bits` counts 1-bits in entire buffer. Because above `resize` doesn't
+        // actually truncate the buffer, `count_set_bits` still return 3.
+        assert_eq!(null_buffer.count_set_bits(), 3);
+        // `count_set_bits_offset` takes len in bits as parameter.
+        assert_eq!(null_buffer.count_set_bits_offset(0, 13), 0);
+
+        let mut data_buffer_builder = BufferBuilder::<i32>::new(13);
+        data_buffer_builder.append_slice(&[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]);
+        let data_buffer = data_buffer_builder.finish();
+
+        let arg1: Int32Array = ArrayDataBuilder::new(DataType::Int32)
+            .len(13)
+            .null_count(13)

Review Comment:
   Should the test skip setting the null count explicitly and instead let the ArrayDataBuilder calculate it?



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