andygrove opened a new pull request, #4911:
URL: https://github.com/apache/datafusion-comet/pull/4911
> This PR was created by an LLM as a draft PR. I will mark it as ready for
review after human review.
## Which issue does this PR close?
N/A — autonomous exploratory PR.
## Rationale for this change
Decimal floor now monomorphizes the per-element op (was &dyn Fn) and
dispatches on input scale to a const divisor with an i64 fast path, so the
per-row 128-bit __divti3 division libcall becomes a multiply-and-shift.
## What changes are included in this PR?
Decimal floor now monomorphizes the per-element op (was &dyn Fn) and
dispatches on input scale to a const divisor with an i64 fast path, so the
per-row 128-bit __divti3 division libcall becomes a multiply-and-shift.
## How are these changes tested?
Correctness: unit tests + seeded differential fuzz (bit-identical Arrow
output vs `main`).
Benchmark (criterion):
- spark_floor_ float64: 10.548% faster (base 1525ns -> cand 1364ns)
- spark_floor_ decimal128(38,6) wide values: 3.043% faster (base 38997ns ->
cand 37810ns)
- spark_floor_ decimal128(38,2): 69.852% faster (base 25462ns -> cand 7676ns)
- spark_floor_ decimal128(38,18): 75.222% faster (base 28693ns -> cand
7109ns)
Full criterion output:
```text
spark_floor: decimal128(38,2)
time: [7.6379 µs 7.6620 µs 7.6869 µs]
change: [−69.961% −69.852% −69.739%] (p = 0.00 <
0.05)
Performance has improved.
spark_floor: decimal128(38,18)
time: [7.0976 µs 7.1216 µs 7.1451 µs]
change: [−75.295% −75.222% −75.141%] (p = 0.00 <
0.05)
Performance has improved.
Found 1 outliers among 100 measurements (1.00%)
1 (1.00%) low mild
spark_floor: decimal128(38,6) wide values
time: [37.480 µs 37.607 µs 37.739 µs]
change: [−3.4647% −3.0427% −2.6266%] (p = 0.00 <
0.05)
Performance has improved.
spark_floor: float64 time: [1.3466 µs 1.3669 µs 1.3899 µs]
change: [−12.450% −10.548% −8.3898%] (p = 0.00 <
0.05)
Performance has improved.
Found 12 outliers among 100 measurements (12.00%)
7 (7.00%) high mild
5 (5.00%) high severe
```
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