bkietz commented on a change in pull request #9294:
URL: https://github.com/apache/arrow/pull/9294#discussion_r571279697
##########
File path: docs/source/cpp/compute.rst
##########
@@ -744,3 +749,34 @@ Structural transforms
* \(2) For each value in the list child array, the index at which it is found
in the list array is appended to the output. Nulls in the parent list array
are discarded.
+
+.. _common-numeric-type:
+
+Common numeric type
+~~~~~~~~~~~~~~~~~~~
+
+The common numeric type of a set of input numeric types is the smallest numeric
+type which can accommodate any value of any input. If any input is a floating
+point type the common numeric type is the widest floating point type among the
+inputs. Otherwise the common numeric type is integral, is signed if any input
+is signed, and its width is the maximum width of any input. For example:
+
++-------------------+----------------------+-------------------------------------------+
+| Input types | Common numeric type | Notes
|
++===================+======================+===========================================+
+| int32, int32 | int32 |
|
++-------------------+----------------------+-------------------------------------------+
+| int16, int32 | int32 | Max width is 32, promote LHS to
int32 |
++-------------------+----------------------+-------------------------------------------+
+| uint16, uint32 | uint32 | All inputs unsigned, maintain
unsigned |
++-------------------+----------------------+-------------------------------------------+
+| uint16, int32 | int32 | One input signed, override
unsigned |
++-------------------+----------------------+-------------------------------------------+
+| int16, uint32 | int32 |
|
Review comment:
@jorisvandenbossche @pitrou I've adopted the suggested behavior of
expanding integer width to accommodate anything except the extreme values of
uint64.
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