emkornfield commented on code in PR #48345: URL: https://github.com/apache/arrow/pull/48345#discussion_r3353535991
########## cpp/src/arrow/util/alp/alp.cc: ########## @@ -0,0 +1,1031 @@ +// 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. + +#include "arrow/util/alp/alp.h" + +#include <cmath> +#include <cstring> +#include <functional> +#include <iostream> +#include <map> + +#include "arrow/util/alp/alp_constants.h" +#include "arrow/util/bit_stream_utils_internal.h" +#include "arrow/util/bit_util.h" +#include "arrow/util/endian.h" +#include "arrow/util/bpacking_internal.h" +#include "arrow/util/logging.h" +#include "arrow/util/span.h" +#include "arrow/util/ubsan.h" + +namespace arrow { +namespace util { +namespace alp { + +// ALP serialization uses memcpy for multi-byte integers (frame_of_reference, +// num_exceptions, offsets) and assumes little-endian byte order on disk. +static_assert(ARROW_LITTLE_ENDIAN, + "ALP serialization assumes little-endian byte order"); + +// ---------------------------------------------------------------------- +// AlpEncodedVectorInfo implementation (non-templated, 4 bytes) + +void AlpEncodedVectorInfo::Store(arrow::util::span<uint8_t> output_buffer) const { + ARROW_CHECK(output_buffer.size() >= static_cast<size_t>(GetStoredSize())) + << "alp_vector_info_output_too_small: " << output_buffer.size() << " vs " + << GetStoredSize(); + + uint8_t* ptr = output_buffer.data(); + + // exponent, factor: 1 byte each + *ptr++ = exponent; + *ptr++ = factor; + + // num_exceptions: 2 bytes + std::memcpy(ptr, &num_exceptions, sizeof(num_exceptions)); +} + +Result<AlpEncodedVectorInfo> AlpEncodedVectorInfo::Load( + arrow::util::span<const uint8_t> input_buffer) { + if (input_buffer.size() < static_cast<size_t>(GetStoredSize())) { + return Status::Invalid("ALP vector info buffer too small: ", input_buffer.size(), + " < ", GetStoredSize()); + } + + AlpEncodedVectorInfo result{}; + const uint8_t* ptr = input_buffer.data(); + + // exponent, factor: 1 byte each + result.exponent = *ptr++; + result.factor = *ptr++; + + // num_exceptions: 2 bytes + std::memcpy(&result.num_exceptions, ptr, sizeof(result.num_exceptions)); + + return result; +} + +// ---------------------------------------------------------------------- +// AlpEncodedForVectorInfo implementation (templated, 5/9 bytes) + +template <typename T> +void AlpEncodedForVectorInfo<T>::Store(arrow::util::span<uint8_t> output_buffer) const { + ARROW_CHECK(output_buffer.size() >= static_cast<size_t>(GetStoredSize())) + << "alp_for_vector_info_output_too_small: " << output_buffer.size() << " vs " + << GetStoredSize(); + + uint8_t* ptr = output_buffer.data(); + + // frame_of_reference: 4 bytes for float, 8 bytes for double + std::memcpy(ptr, &frame_of_reference, sizeof(frame_of_reference)); + ptr += sizeof(frame_of_reference); + + // bit_width: 1 byte + *ptr = bit_width; +} + +template <typename T> +Result<AlpEncodedForVectorInfo<T>> AlpEncodedForVectorInfo<T>::Load( + arrow::util::span<const uint8_t> input_buffer) { + if (input_buffer.size() < static_cast<size_t>(GetStoredSize())) { + return Status::Invalid("ALP FOR vector info buffer too small: ", input_buffer.size(), + " < ", GetStoredSize()); + } + + AlpEncodedForVectorInfo<T> result{}; + const uint8_t* ptr = input_buffer.data(); + + // frame_of_reference: 4 bytes for float, 8 bytes for double + std::memcpy(&result.frame_of_reference, ptr, sizeof(result.frame_of_reference)); + ptr += sizeof(result.frame_of_reference); + + // bit_width: 1 byte + result.bit_width = *ptr; + + return result; +} + +// Explicit template instantiations for AlpEncodedForVectorInfo +template struct AlpEncodedForVectorInfo<float>; +template struct AlpEncodedForVectorInfo<double>; + +// ---------------------------------------------------------------------- +// AlpEncodedVector implementation + +template <typename T> +void AlpEncodedVector<T>::Store(arrow::util::span<uint8_t> output_buffer) const { + const int64_t overall_size = GetStoredSize(); + ARROW_CHECK(static_cast<int64_t>(output_buffer.size()) >= overall_size) + << "alp_bit_packed_vector_store_output_too_small: " << output_buffer.size() + << " vs " << overall_size; + + int64_t offset = 0; + + // Store AlpInfo (4 bytes) + alp_info.Store({output_buffer.data() + offset, AlpEncodedVectorInfo::kStoredSize}); + offset += AlpEncodedVectorInfo::kStoredSize; + + // Store ForInfo (6/10 bytes) Review Comment: 5 or 9? maybe just remove the detail? ```suggestion // Store ForInfo ``` -- This is an automated message from the Apache Git Service. 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