[jira] [Created] (ARROW-786) [Format] In-memory format for 128-bit Decimals, handling of sign bit

["Wes McKinney (JIRA)" <ji...@apache.org>]

Wes McKinney created ARROW-786:
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             Summary: [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


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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