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/*
* Copyright (c) 2016-present, Facebook, Inc.
* All rights reserved.
*
* This source code is licensed under both the BSD-style license (found in the
* LICENSE file in the root directory of this source tree) and the GPLv2 (found
* in the COPYING file in the root directory of this source tree).
*/
#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_;
}
};
}
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