[jira] [Commented] (ARROW-13096) [C++] Implement logarithm compute functions

["Eduardo Ponce (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-13096?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17367085#comment-17367085 ] 

Eduardo Ponce commented on ARROW-13096:
---------------------------------------

I consider having (1) *ln*, (2) *log10*, and (3) *log2* is a good starting point, and the missing variants are:
 (4) *log\(x, base)* = *log\(x)* / *log(base)*, note that *log(base)* is a constant w.r.t. to Datum *x* so optimizations can be made
 (5) *log1p\(x)* = *log(1+x)*

Note that (4) is the most general variant as it can represent any of the other variants, so it might be worthwhile to consider adding it to Arrow.

As additional context, here is the partial landscape of log functions across library/languages:
 * [C++ math library|https://www.cplusplus.com/reference/cmath/log] supports (1,2,3,5)
 * [Python *math* module|https://docs.python.org/3/library/math.html#math.log] supports (1-5)
 * [Python *numpy*|https://numpy.org/doc/stable/reference/generated/numpy.log.html#numpy.log] supports (1,2,3,5)
 * [R|https://www.rdocumentation.org/packages/base/versions/3.6.2/topics/log] supports (1-5)
 * [Rust math|https://docs.rs/numeric/0.1.4/numeric/math/fn.log.html] support (1-5)
 * [MySQL|https://dev.mysql.com/doc/refman/8.0/en/mathematical-functions.html] supports (1-4)
 * [PostgreSQL|https://www.postgresql.org/docs/9.1/functions-math.html] supports (1,2,4)

> [C++] Implement logarithm compute functions
> -------------------------------------------
>
>                 Key: ARROW-13096
>                 URL: https://issues.apache.org/jira/browse/ARROW-13096
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: C++
>            Reporter: David Li
>            Assignee: David Li
>            Priority: Major
>              Labels: beginner, pull-request-available
>          Time Spent: 1h 50m
>  Remaining Estimate: 0h
>
> ln, log, log2?



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