andygrove commented on code in PR #23471:
URL: https://github.com/apache/datafusion/pull/23471#discussion_r3574014085
##########
datafusion/functions/src/math/round.rs:
##########
@@ -859,15 +845,84 @@ fn round_integer_array(
}
}
-fn round_float<T>(value: T, decimal_places: i32) -> Result<T, ArrowError>
+/// Rounds a float array to `decimal_places`, taking the hoisted-factor fast
+/// path when it applies and falling back to the shared binary-math kernel
+/// otherwise.
+fn round_float_column<PT>(
+ value_array: &ArrayRef,
+ decimal_places: &ColumnarValue,
+) -> Result<ArrayRef>
where
- T: num_traits::Float,
+ PT: ArrowPrimitiveType,
+ PT::Native: num_traits::Float,
{
- let factor = T::from(10_f64.powi(decimal_places)).ok_or_else(|| {
+ if let Some(arr) = round_float_fast::<PT>(value_array, decimal_places)? {
+ return Ok(arr);
+ }
+ let result = calculate_binary_math::<PT, Int32Type, PT, _>(
+ value_array.as_ref(),
+ decimal_places,
+ round_float::<PT::Native>,
+ )?;
+ Ok(result as _)
+}
+
+/// Fast path for rounding a float array to a scalar number of
`decimal_places`.
+///
+/// The shared `calculate_binary_math` kernel routes through `try_unary` and
+/// re-evaluates `round_float` (including `10f64.powi(decimal_places)` and a
+/// `Result` check) for every element. When `decimal_places` is a non-null
+/// scalar and the value column has no nulls, we can hoist the scaling factor
+/// out of the loop and use the infallible `unary` kernel instead, which the
+/// compiler can autovectorize. Requiring no null slots keeps the output
+/// bit-identical to the fallible kernel: `unary` writes a computed value into
+/// every slot while `try_unary` leaves null slots zeroed, so the two only
agree
+/// when there are no null slots. Returns `Ok(None)` when the fast path does
not
Review Comment:
Good point. Thanks, I fixed that.
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