1 //===- BinaryItemStream.h ---------------------------------------*- C++ -*-===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #ifndef LLVM_SUPPORT_BINARYITEMSTREAM_H
11 #define LLVM_SUPPORT_BINARYITEMSTREAM_H
12 
13 #include "llvm/ADT/ArrayRef.h"
14 #include "llvm/Support/BinaryStream.h"
15 #include "llvm/Support/BinaryStreamError.h"
16 #include "llvm/Support/Error.h"
17 #include <cstddef>
18 #include <cstdint>
19 
20 namespace llvm {
21 
22 template <typename T> struct BinaryItemTraits {
23   static size_t length(const T &Item) = delete;
24   static ArrayRef<uint8_t> bytes(const T &Item) = delete;
25 };
26 
27 /// BinaryItemStream represents a sequence of objects stored in some kind of
28 /// external container but for which it is useful to view as a stream of
29 /// contiguous bytes.  An example of this might be if you have a collection of
30 /// records and you serialize each one into a buffer, and store these serialized
31 /// records in a container.  The pointers themselves are not laid out
32 /// contiguously in memory, but we may wish to read from or write to these
33 /// records as if they were.
34 template <typename T, typename Traits = BinaryItemTraits<T>>
35 class BinaryItemStream : public BinaryStream {
36 public:
BinaryItemStream(llvm::support::endianness Endian)37   explicit BinaryItemStream(llvm::support::endianness Endian)
38       : Endian(Endian) {}
39 
getEndian()40   llvm::support::endianness getEndian() const override { return Endian; }
41 
readBytes(uint32_t Offset,uint32_t Size,ArrayRef<uint8_t> & Buffer)42   Error readBytes(uint32_t Offset, uint32_t Size,
43                   ArrayRef<uint8_t> &Buffer) override {
44     auto ExpectedIndex = translateOffsetIndex(Offset);
45     if (!ExpectedIndex)
46       return ExpectedIndex.takeError();
47     const auto &Item = Items[*ExpectedIndex];
48     if (auto EC = checkOffsetForRead(Offset, Size))
49       return EC;
50     if (Size > Traits::length(Item))
51       return make_error<BinaryStreamError>(stream_error_code::stream_too_short);
52     Buffer = Traits::bytes(Item).take_front(Size);
53     return Error::success();
54   }
55 
readLongestContiguousChunk(uint32_t Offset,ArrayRef<uint8_t> & Buffer)56   Error readLongestContiguousChunk(uint32_t Offset,
57                                    ArrayRef<uint8_t> &Buffer) override {
58     auto ExpectedIndex = translateOffsetIndex(Offset);
59     if (!ExpectedIndex)
60       return ExpectedIndex.takeError();
61     Buffer = Traits::bytes(Items[*ExpectedIndex]);
62     return Error::success();
63   }
64 
setItems(ArrayRef<T> ItemArray)65   void setItems(ArrayRef<T> ItemArray) {
66     Items = ItemArray;
67     computeItemOffsets();
68   }
69 
getLength()70   uint32_t getLength() override {
71     return ItemEndOffsets.empty() ? 0 : ItemEndOffsets.back();
72   }
73 
74 private:
computeItemOffsets()75   void computeItemOffsets() {
76     ItemEndOffsets.clear();
77     ItemEndOffsets.reserve(Items.size());
78     uint32_t CurrentOffset = 0;
79     for (const auto &Item : Items) {
80       uint32_t Len = Traits::length(Item);
81       assert(Len > 0 && "no empty items");
82       CurrentOffset += Len;
83       ItemEndOffsets.push_back(CurrentOffset);
84     }
85   }
86 
translateOffsetIndex(uint32_t Offset)87   Expected<uint32_t> translateOffsetIndex(uint32_t Offset) {
88     // Make sure the offset is somewhere in our items array.
89     if (Offset >= getLength())
90       return make_error<BinaryStreamError>(stream_error_code::stream_too_short);
91     ++Offset;
92     auto Iter =
93         std::lower_bound(ItemEndOffsets.begin(), ItemEndOffsets.end(), Offset);
94     size_t Idx = std::distance(ItemEndOffsets.begin(), Iter);
95     assert(Idx < Items.size() && "binary search for offset failed");
96     return Idx;
97   }
98 
99   llvm::support::endianness Endian;
100   ArrayRef<T> Items;
101 
102   // Sorted vector of offsets to accelerate lookup.
103   std::vector<uint32_t> ItemEndOffsets;
104 };
105 
106 } // end namespace llvm
107 
108 #endif // LLVM_SUPPORT_BINARYITEMSTREAM_H
109