seddonm1 commented on a change in pull request #9509: URL: https://github.com/apache/arrow/pull/9509#discussion_r577298518
########## File path: rust/arrow/src/compute/kernels/bit_length.rs ########## @@ -0,0 +1,208 @@ +// 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 kernel for length of a string array + +use crate::{array::*, buffer::Buffer}; +use crate::{ + datatypes::DataType, + error::{ArrowError, Result}, +}; +use std::sync::Arc; + +fn bit_length_string<OffsetSize>(array: &Array, data_type: DataType) -> ArrayRef +where + OffsetSize: OffsetSizeTrait, +{ + // note: offsets are stored as u8, but they can be interpreted as OffsetSize + let offsets = &array.data_ref().buffers()[0]; + // this is a 30% improvement over iterating over u8s and building OffsetSize, which + // justifies the usage of `unsafe`. + let slice: &[OffsetSize] = + &unsafe { offsets.typed_data::<OffsetSize>() }[array.offset()..]; + + let bit_size = OffsetSize::from_usize(8).unwrap(); + let lengths = slice + .windows(2) + .map(|offset| (offset[1] - offset[0]) * bit_size); + + // JUSTIFICATION + // Benefit + // ~60% speedup + // Soundness + // `values` is an iterator with a known size. + let buffer = unsafe { Buffer::from_trusted_len_iter(lengths) }; + Review comment: yes i can have a look at doing that. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected]
