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Posted to jira@arrow.apache.org by "Wes McKinney (Jira)" <ji...@apache.org> on 2020/09/06 18:01:00 UTC
[jira] [Updated] (ARROW-9913) [C++] Outputs of
Decimal128::FromString depend on presence of one another
[ https://issues.apache.org/jira/browse/ARROW-9913?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Wes McKinney updated ARROW-9913:
--------------------------------
Summary: [C++] Outputs of Decimal128::FromString depend on presence of one another (was: Outputs of Decimal128::FromString depend on presence of one another)
> [C++] Outputs of Decimal128::FromString depend on presence of one another
> -------------------------------------------------------------------------
>
> Key: ARROW-9913
> URL: https://issues.apache.org/jira/browse/ARROW-9913
> Project: Apache Arrow
> Issue Type: Bug
> Components: C++
> Reporter: Mingyu Zhong
> Assignee: Mingyu Zhong
> Priority: Minor
> Labels: pull-request-available
> Time Spent: 40m
> Remaining Estimate: 0h
>
> [https://github.com/apache/arrow/blame/bfac60dd73bffa5f7bcefc890486268036182278/cpp/src/arrow/util/decimal.cc#L365-L373] in Decimal128::FromString makes *out depend on whether scale is null, and makes *scale depend on whether out is null. For example, given an input "1e2",
> # if out is not null and scale is not null, then *out is 1
> # if out is null and scale is not null, then *scale is -2
> # if neither out nor scale is null, then *out is 100 and *scale is 0
> It is very counter-intuitive that when an additional output-only pointer is given for receiving extra info, it alters the value of another output.
> Similarly, *precision is also affected by presence of out and scale.
> The block of adjustment was added in [https://github.com/apache/arrow/commit/bfac60dd73bffa5f7bcefc890486268036182278] for preventing negative scale output (https://issues.apache.org/jira/browse/ARROW-2177). While the motivation looks reasonable, the change is not sufficient (see case #2 above).
> I think we should make the outputs independent of one-another. For the input "1e2", *out should be 100 if out is not null, and *scale should be 0 if scale is not null.
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