emkornfield commented on code in PR #48345: URL: https://github.com/apache/arrow/pull/48345#discussion_r2722284815
########## cpp/src/arrow/util/alp/alp_wrapper.h: ########## @@ -0,0 +1,148 @@ +// 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. + +// High-level wrapper interface for ALP compression + +#pragma once + +#include <cstddef> +#include <optional> + +#include "arrow/util/alp/alp.h" + +namespace arrow { +namespace util { +namespace alp { + +// ---------------------------------------------------------------------- +// AlpWrapper + +/// \class AlpWrapper +/// \brief High-level interface for ALP compression +/// +/// AlpWrapper is an interface for Adaptive Lossless floating-Point Compression +/// (ALP) (https://dl.acm.org/doi/10.1145/3626717). For encoding, it samples +/// the data and applies decimal compression (Alp) to floating point values. +/// This class acts as a wrapper around the vector-based interfaces of +/// AlpSampler and Alp. +/// +/// \tparam T the floating point type (float or double) +template <typename T> +class AlpWrapper { + public: + /// \brief Encode floating point values using ALP decimal compression + /// + /// \param[in] decomp pointer to the input that is to be encoded + /// \param[in] decomp_size size of decomp in bytes. + /// This needs to be a multiple of sizeof(T). + /// \param[out] comp pointer to the memory region we will encode into. + /// The caller is responsible for ensuring this is big enough. + /// \param[in,out] comp_size the actual size of the encoded data in bytes, + /// expects the size of comp as input. If this is too small, + /// this is set to 0 and we bail out. + /// \param[in] enforce_mode reserved for future use. + /// Currently only AlpMode::kAlp is supported. + static void Encode(const T* decomp, size_t decomp_size, char* comp, + size_t* comp_size, + std::optional<AlpMode> enforce_mode = std::nullopt); + + /// \brief Decode floating point values + /// + /// \param[out] decomp pointer to the memory region we will decode into. + /// The caller is responsible for ensuring this is big enough + /// to hold num_elements values. + /// \param[in] num_elements number of elements to decode (from page header). + /// Uses uint32_t since Parquet page headers use i32 for num_values. + /// \param[in] comp pointer to the input that is to be decoded + /// \param[in] comp_size size of the input in bytes (from page header) + /// \tparam TargetType the type that is used to store the output. + /// May not be a narrowing conversion from T. + template <typename TargetType> + static void Decode(TargetType* decomp, uint32_t num_elements, const char* comp, + size_t comp_size); + + /// \brief Get the maximum compressed size of an uncompressed buffer + /// + /// \param[in] decomp_size the size of the uncompressed buffer in bytes + /// \return the maximum size of the compressed buffer + static uint64_t GetMaxCompressedSize(uint64_t decomp_size); + + private: + struct AlpHeader; + + /// \brief Tracks the progress of a compression operation + /// + /// Used to report how much data was consumed and produced during encoding. + struct CompressionProgress { + /// Number of compressed bytes written to output + uint64_t num_compressed_bytes_produced = 0; + /// Number of input elements consumed + uint64_t num_uncompressed_elements_taken = 0; + }; + + /// \brief Tracks the progress of a decompression operation + /// + /// Used to report how much data was consumed and produced during decoding. + struct DecompressionProgress { + /// Number of decompressed elements written + uint64_t num_decompressed_elements_produced = 0; + /// Number of compressed bytes consumed + uint64_t num_compressed_bytes_taken = 0; + }; + + /// \brief Compress a buffer using the ALP variant + /// + /// \param[in] decomp array of floating point numbers to compress + /// \param[in] element_count the number of floating point numbers + /// \param[out] comp the buffer to be compressed into + /// \param[in] comp_size the size of the compression buffer + /// \param[in] combinations the encoding preset to use + /// \return the compression progress + static CompressionProgress EncodeAlp(const T* decomp, uint64_t element_count, + char* comp, size_t comp_size, + const AlpEncodingPreset& combinations); + + /// \brief Decompress a buffer using the ALP variant + /// + /// \param[out] decomp the buffer to be decompressed into Review Comment: nit: style out parameters go last -- This is an automated message from the Apache Git Service. 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