[GitHub] [arrow] nevi-me commented on a change in pull request #9297: ARROW-11354: [Rust] Speed-up cast of dates and times (2-4x)

[GitBox <gi...@apache.org>]

nevi-me commented on a change in pull request #9297:
URL: https://github.com/apache/arrow/pull/9297#discussion_r563288134



##########
File path: rust/arrow/src/compute/kernels/unary.rs
##########
@@ -0,0 +1,74 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! Defines kernels suitable to perform unary operations to primitive arrays.
+
+use crate::array::{Array, ArrayData, PrimitiveArray};
+use crate::buffer::Buffer;
+use crate::datatypes::ArrowPrimitiveType;
+
+#[inline]
+fn into_primitive_array_data<I: ArrowPrimitiveType, O: ArrowPrimitiveType>(
+    array: &PrimitiveArray<I>,
+    buffer: Buffer,
+) -> ArrayData {
+    ArrayData::new(
+        O::DATA_TYPE,
+        array.len(),
+        None,

Review comment:
       We could save a further few cycles here by specifying the null count, as it's known and trusted to be correct.

##########
File path: rust/arrow/src/compute/kernels/unary.rs
##########
@@ -0,0 +1,74 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! Defines kernels suitable to perform unary operations to primitive arrays.
+
+use crate::array::{Array, ArrayData, PrimitiveArray};
+use crate::buffer::Buffer;
+use crate::datatypes::ArrowPrimitiveType;
+
+#[inline]
+fn into_primitive_array_data<I: ArrowPrimitiveType, O: ArrowPrimitiveType>(
+    array: &PrimitiveArray<I>,
+    buffer: Buffer,
+) -> ArrayData {
+    ArrayData::new(
+        O::DATA_TYPE,
+        array.len(),
+        None,
+        array.data_ref().null_buffer().cloned(),
+        0,
+        vec![buffer],
+        vec![],
+    )
+}
+
+/// Applies an unary and infalible function to a primitive array.
+/// This is the fastest way to perform an operation on a primitive array when
+/// the benefits of a vectorized operation outweights the cost of branching nulls and non-nulls.
+/// # Implementation
+/// This will apply the function for all values, including those on null slots.
+/// This implies that the operation must be infalible for any value of the corresponding type
+/// or this function may panic.
+/// # Example
+/// ```rust
+/// # use arrow::array::Int32Array;
+/// # use arrow::datatypes::Int32Type;
+/// # use arrow::compute::kernels::unary::unary;
+/// # fn main() {
+/// let array = Int32Array::from(vec![Some(5), Some(7), None]);
+/// let c = unary::<_, _, Int32Type>(&array, |x| x * 2 + 1);
+/// assert_eq!(c, Int32Array::from(vec![Some(11), Some(15), None]));

Review comment:
       This is a great and simple example, and I wonder if the compiler is smart enough to optimise 2 commutative unary functions to perform as well as a single combined one.
   
   Worth trying out some time.




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