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https://issues.apache.org/jira/browse/ARROW-4186?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17661210#comment-17661210
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Rok Mihevc commented on ARROW-4186:
-----------------------------------
This issue has been migrated to [issue
#20769|https://github.com/apache/arrow/issues/20769] on GitHub. Please see the
[migration documentation|https://github.com/apache/arrow/issues/14542] for
further details.
> [C++] BitmapWriters clobber the first byte when length=0
> --------------------------------------------------------
>
> Key: ARROW-4186
> URL: https://issues.apache.org/jira/browse/ARROW-4186
> Project: Apache Arrow
> Issue Type: Bug
> Components: C++
> Reporter: Ben Kietzman
> Assignee: Antoine Pitrou
> Priority: Minor
> Labels: pull-request-available
> Fix For: 0.12.0
>
> Time Spent: 40m
> Remaining Estimate: 0h
>
> When a BitmapWriter or FirstTimeBitmapWriter is constructed with length=0
> then Finish() is invoked, the byte at {{start_offset / 8}} is zeroed
> The following change causes the test to fail:
> {code}
> --- a/cpp/src/arrow/util/bit-util-test.cc
> +++ b/cpp/src/arrow/util/bit-util-test.cc
> @@ -274,6 +274,10 @@ TEST(FirstTimeBitmapWriter, NormalOperation) {
> auto writer = internal::FirstTimeBitmapWriter(bitmap, 10, 3);
> WriteVectorToWriter(writer, {0, 0, 0});
> }
> + {
> + auto writer = internal::FirstTimeBitmapWriter(bitmap, 13, 0);
> + WriteVectorToWriter(writer, {});
> + }
> {
> auto writer = internal::FirstTimeBitmapWriter(bitmap, 13, 3);
> WriteVectorToWriter(writer, {1, 0, 1});
> {code}
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