pitrou opened a new pull request, #45217:
URL: https://github.com/apache/arrow/pull/45217
### Rationale for this change
The Rank implementation currently mixes ties/duplicates detection and rank
computation in a single function `CreateRankings`. This makes it poorly
reusable for other Rank-like functions such as the Percentile Rank function
proposed in GH-45190.
### What changes are included in this PR?
Split duplicates detection into a dedicated function that sets a marker bit
in the sort-indices array (it is private to the Rank implementation, so it is
safe to mutate it).
The rank computation itself (`CreateRankings`) becomes simpler and,
moreover, it does not need to read the input values: it becomes therefore
type-agnostic.
This yields a code size reduction (around 45kB saved on the author's
machine):
* before:
```console
$ size /build/build-release/relwithdebinfo/libarrow.so
text data bss dec hex filename
26072218 353832 2567985 28994035 1ba69f3
/build/build-release/relwithdebinfo/libarrow.so
```
* after:
```console
$ size /build/build-release/relwithdebinfo/libarrow.so
text data bss dec hex filename
26028198 353832 2567985 28950015 1b9bdff
/build/build-release/relwithdebinfo/libarrow.so
```
Rank benchmark results are mostly neutral, though there are slight
improvements on some benchmarks, and slight regressions especially on all-nulls
input.
### Are these changes tested?
Yes, by existing tests.
### Are there any user-facing changes?
No.
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