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11fdf7f2 | 1 | /* |
7c673cae FG |
2 | * Copyright (c) 2016-present, Facebook, Inc. |
3 | * All rights reserved. | |
4 | * | |
11fdf7f2 TL |
5 | * This source code is licensed under both the BSD-style license (found in the |
6 | * LICENSE file in the root directory of this source tree) and the GPLv2 (found | |
7 | * in the COPYING file in the root directory of this source tree). | |
7c673cae FG |
8 | */ |
9 | #pragma once | |
10 | ||
11 | #include "utils/Range.h" | |
12 | ||
13 | #include <array> | |
14 | #include <cstddef> | |
15 | #include <cstdint> | |
16 | #include <cstdio> | |
17 | ||
18 | namespace pzstd { | |
19 | /** | |
20 | * We put a skippable frame before each frame. | |
21 | * It contains a skippable frame magic number, the size of the skippable frame, | |
22 | * and the size of the next frame. | |
23 | * Each skippable frame is exactly 12 bytes in little endian format. | |
24 | * The first 8 bytes are for compatibility with the ZSTD format. | |
25 | * If we have N threads, the output will look like | |
26 | * | |
27 | * [0x184D2A50|4|size1] [frame1 of size size1] | |
28 | * [0x184D2A50|4|size2] [frame2 of size size2] | |
29 | * ... | |
30 | * [0x184D2A50|4|sizeN] [frameN of size sizeN] | |
31 | * | |
32 | * Each sizeX is 4 bytes. | |
33 | * | |
34 | * These skippable frames should allow us to skip through the compressed file | |
35 | * and only load at most N pages. | |
36 | */ | |
37 | class SkippableFrame { | |
38 | public: | |
39 | static constexpr std::size_t kSize = 12; | |
40 | ||
41 | private: | |
42 | std::uint32_t frameSize_; | |
43 | std::array<std::uint8_t, kSize> data_; | |
44 | static constexpr std::uint32_t kSkippableFrameMagicNumber = 0x184D2A50; | |
45 | // Could be improved if the size fits in less bytes | |
46 | static constexpr std::uint32_t kFrameContentsSize = kSize - 8; | |
47 | ||
48 | public: | |
49 | // Write the skippable frame to data_ in LE format. | |
50 | explicit SkippableFrame(std::uint32_t size); | |
51 | ||
52 | // Read the skippable frame from bytes in LE format. | |
53 | static std::size_t tryRead(ByteRange bytes); | |
54 | ||
55 | ByteRange data() const { | |
56 | return {data_.data(), data_.size()}; | |
57 | } | |
58 | ||
59 | // Size of the next frame. | |
60 | std::size_t frameSize() const { | |
61 | return frameSize_; | |
62 | } | |
63 | }; | |
64 | } |