| /** |
| * Copyright (c) 2016-present, Facebook, Inc. |
| * All rights reserved. |
| * |
| * This source code is licensed under the BSD-style license found in the |
| * LICENSE file in the root directory of this source tree. An additional grant |
| * of patent rights can be found in the PATENTS file in the same directory. |
| */ |
| #pragma once |
| |
| #include "utils/Range.h" |
| |
| #include <array> |
| #include <cstddef> |
| #include <cstdint> |
| #include <cstdio> |
| |
| namespace pzstd { |
| /** |
| * We put a skippable frame before each frame. |
| * It contains a skippable frame magic number, the size of the skippable frame, |
| * and the size of the next frame. |
| * Each skippable frame is exactly 12 bytes in little endian format. |
| * The first 8 bytes are for compatibility with the ZSTD format. |
| * If we have N threads, the output will look like |
| * |
| * [0x184D2A50|4|size1] [frame1 of size size1] |
| * [0x184D2A50|4|size2] [frame2 of size size2] |
| * ... |
| * [0x184D2A50|4|sizeN] [frameN of size sizeN] |
| * |
| * Each sizeX is 4 bytes. |
| * |
| * These skippable frames should allow us to skip through the compressed file |
| * and only load at most N pages. |
| */ |
| class SkippableFrame { |
| public: |
| static constexpr std::size_t kSize = 12; |
| |
| private: |
| std::uint32_t frameSize_; |
| std::array<std::uint8_t, kSize> data_; |
| static constexpr std::uint32_t kSkippableFrameMagicNumber = 0x184D2A50; |
| // Could be improved if the size fits in less bytes |
| static constexpr std::uint32_t kFrameContentsSize = kSize - 8; |
| |
| public: |
| // Write the skippable frame to data_ in LE format. |
| explicit SkippableFrame(std::uint32_t size); |
| |
| // Read the skippable frame from bytes in LE format. |
| static std::size_t tryRead(ByteRange bytes); |
| |
| ByteRange data() const { |
| return {data_.data(), data_.size()}; |
| } |
| |
| // Size of the next frame. |
| std::size_t frameSize() const { |
| return frameSize_; |
| } |
| }; |
| } |