1 | //===- BinaryItemStream.h ---------------------------------------*- C++ -*-===// |
2 | // |
3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
4 | // See https://llvm.org/LICENSE.txt for license information. |
5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
6 | // |
7 | //===----------------------------------------------------------------------===// |
8 | |
9 | #ifndef LLVM_SUPPORT_BINARYITEMSTREAM_H |
10 | #define LLVM_SUPPORT_BINARYITEMSTREAM_H |
11 | |
12 | #include "llvm/ADT/ArrayRef.h" |
13 | #include "llvm/Support/BinaryStream.h" |
14 | #include "llvm/Support/BinaryStreamError.h" |
15 | #include "llvm/Support/Error.h" |
16 | #include <cstddef> |
17 | #include <cstdint> |
18 | |
19 | namespace llvm { |
20 | |
21 | template <typename T> struct BinaryItemTraits { |
22 | static size_t length(const T &Item) = delete; |
23 | static ArrayRef<uint8_t> bytes(const T &Item) = delete; |
24 | }; |
25 | |
26 | /// BinaryItemStream represents a sequence of objects stored in some kind of |
27 | /// external container but for which it is useful to view as a stream of |
28 | /// contiguous bytes. An example of this might be if you have a collection of |
29 | /// records and you serialize each one into a buffer, and store these serialized |
30 | /// records in a container. The pointers themselves are not laid out |
31 | /// contiguously in memory, but we may wish to read from or write to these |
32 | /// records as if they were. |
33 | template <typename T, typename Traits = BinaryItemTraits<T>> |
34 | class BinaryItemStream : public BinaryStream { |
35 | public: |
36 | explicit BinaryItemStream(llvm::endianness Endian) : Endian(Endian) {} |
37 | |
38 | llvm::endianness getEndian() const override { return Endian; } |
39 | |
40 | Error readBytes(uint64_t Offset, uint64_t Size, |
41 | ArrayRef<uint8_t> &Buffer) override { |
42 | auto ExpectedIndex = translateOffsetIndex(Offset); |
43 | if (!ExpectedIndex) |
44 | return ExpectedIndex.takeError(); |
45 | const auto &Item = Items[*ExpectedIndex]; |
46 | if (auto EC = checkOffsetForRead(Offset, DataSize: Size)) |
47 | return EC; |
48 | if (Size > Traits::length(Item)) |
49 | return make_error<BinaryStreamError>(Args: stream_error_code::stream_too_short); |
50 | Buffer = Traits::bytes(Item).take_front(Size); |
51 | return Error::success(); |
52 | } |
53 | |
54 | Error readLongestContiguousChunk(uint64_t Offset, |
55 | ArrayRef<uint8_t> &Buffer) override { |
56 | auto ExpectedIndex = translateOffsetIndex(Offset); |
57 | if (!ExpectedIndex) |
58 | return ExpectedIndex.takeError(); |
59 | Buffer = Traits::bytes(Items[*ExpectedIndex]); |
60 | return Error::success(); |
61 | } |
62 | |
63 | void setItems(ArrayRef<T> ItemArray) { |
64 | Items = ItemArray; |
65 | computeItemOffsets(); |
66 | } |
67 | |
68 | uint64_t getLength() override { |
69 | return ItemEndOffsets.empty() ? 0 : ItemEndOffsets.back(); |
70 | } |
71 | |
72 | private: |
73 | void computeItemOffsets() { |
74 | ItemEndOffsets.clear(); |
75 | ItemEndOffsets.reserve(n: Items.size()); |
76 | uint64_t CurrentOffset = 0; |
77 | for (const auto &Item : Items) { |
78 | uint64_t Len = Traits::length(Item); |
79 | assert(Len > 0 && "no empty items" ); |
80 | CurrentOffset += Len; |
81 | ItemEndOffsets.push_back(x: CurrentOffset); |
82 | } |
83 | } |
84 | |
85 | Expected<uint32_t> translateOffsetIndex(uint64_t Offset) { |
86 | // Make sure the offset is somewhere in our items array. |
87 | if (Offset >= getLength()) |
88 | return make_error<BinaryStreamError>(Args: stream_error_code::stream_too_short); |
89 | ++Offset; |
90 | auto Iter = llvm::lower_bound(Range&: ItemEndOffsets, Value&: Offset); |
91 | size_t Idx = std::distance(first: ItemEndOffsets.begin(), last: Iter); |
92 | assert(Idx < Items.size() && "binary search for offset failed" ); |
93 | return Idx; |
94 | } |
95 | |
96 | llvm::endianness Endian; |
97 | ArrayRef<T> Items; |
98 | |
99 | // Sorted vector of offsets to accelerate lookup. |
100 | std::vector<uint64_t> ItemEndOffsets; |
101 | }; |
102 | |
103 | } // end namespace llvm |
104 | |
105 | #endif // LLVM_SUPPORT_BINARYITEMSTREAM_H |
106 | |