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