1 //===- BinaryItemStream.h ---------------------------------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 #ifndef LLVM_SUPPORT_BINARYITEMSTREAM_H
11 #define LLVM_SUPPORT_BINARYITEMSTREAM_H
13 #include "llvm/ADT/ArrayRef.h"
14 #include "llvm/Support/BinaryStream.h"
15 #include "llvm/Support/BinaryStreamError.h"
16 #include "llvm/Support/Error.h"
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;
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 {
37 explicit BinaryItemStream(llvm::support::endianness Endian)
40 llvm::support::endianness getEndian() const override { return Endian; }
42 Error readBytes(uint32_t Offset, uint32_t Size,
43 ArrayRef<uint8_t> &Buffer) override {
44 auto ExpectedIndex = translateOffsetIndex(Offset);
46 return ExpectedIndex.takeError();
47 const auto &Item = Items[*ExpectedIndex];
48 if (auto EC = checkOffset(Offset, Size))
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();
56 Error readLongestContiguousChunk(uint32_t Offset,
57 ArrayRef<uint8_t> &Buffer) override {
58 auto ExpectedIndex = translateOffsetIndex(Offset);
60 return ExpectedIndex.takeError();
61 Buffer = Traits::bytes(Items[*ExpectedIndex]);
62 return Error::success();
65 void setItems(ArrayRef<T> ItemArray) {
70 uint32_t getLength() override {
71 return ItemEndOffsets.empty() ? 0 : ItemEndOffsets.back();
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");
83 ItemEndOffsets.push_back(CurrentOffset);
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);
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");
99 llvm::support::endianness Endian;
102 // Sorted vector of offsets to accelerate lookup.
103 std::vector<uint32_t> ItemEndOffsets;
106 } // end namespace llvm
108 #endif // LLVM_SUPPORT_BINARYITEMSTREAM_H