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https://issues.apache.org/jira/browse/ARROW-786?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16102037#comment-16102037
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Wes McKinney commented on ARROW-786:
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It seems like we might end up having to build a from-scratch implementation of
Java's BigDecimal in C++. It might be worth it, but it's also a lot of work.
The JDK source code is not ASF-friendly so we would have to start from scratch
from a mathematical resource
> [Format] In-memory format for 128-bit Decimals, handling of sign bit
> --------------------------------------------------------------------
>
> Key: ARROW-786
> URL: https://issues.apache.org/jira/browse/ARROW-786
> Project: Apache Arrow
> Issue Type: Improvement
> Components: Format
> Reporter: Wes McKinney
> Fix For: 0.6.0
>
>
> cc [~cpcloud]
> We found in ARROW-655 that we needed to add an extra bit for signedness for
> decimals stored as 128-bit values to be able to use the Boost multiprecision
> libraries. This makes Decimal128 not fit completely neatly as a 16-byte fixed
> size binary value, and more of a {{struct<sign_bitmap: boolean, data:
> fixed_size_binary(16)>}}. What is the current formata in the Java
> implementation? We will need to document the memory layout for decimals that
> maximizes compatibility across languages and eventually implement integration
> tests for IPC.
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