Mingyu Zhong created ARROW-9913: ----------------------------------- Summary: 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
[This block|[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. -- This message was sent by Atlassian Jira (v8.3.4#803005)