[ARROW-1749] [C++] Handle range of Decimal128 values that require 39 digits to be displayed

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.7.1
• Fix Version/s: 0.8.0
• Component/s: C++
• Labels: pull-request-available
• External issue URL: https://github.com/apache/arrow/issues/17752
• Assignee: Phillip Cloud
• Reporter: Phillip Cloud
• Created: 28/Oct/17 17:29
• Updated: 11/Jan/23 07:16
• Resolved: 05/Nov/17 23:51

Description

2 ** 127 - 1 and -2 ** 127 both require a 39th digit to be displayed as a decimal string.

This means we do not have the ability to display decimal values above 10 ** 38 - 1 even though we have the ability to store them.

For reference, Impala returns NULL when trying to cast 2 ** 127 - 1 to DECIMAL(38, 0).

A few next steps are in order:

1. Explicitly test this behavior
2. Avoid crashing or displaying garbage when we cannot display a number that can be stored
3. Make a decision about whether we want to eventually support range of values from 10 ** 38 to 2 ** 127 - 1 positive and -2 ** 127 to -10 ** 38 negative. This would require a larger integer type to hold the value just before being converted to a string.

Issue Links

• links to: GitHub Pull Request #1282