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      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:
     37   explicit BinaryItemStream(llvm::support::endianness Endian)
     38       : Endian(Endian) {}
     39 
     40   llvm::support::endianness getEndian() const override { return Endian; }
     41 
     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 = checkOffset(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 
     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 
     65   void setItems(ArrayRef<T> ItemArray) {
     66     Items = ItemArray;
     67     computeItemOffsets();
     68   }
     69 
     70   uint32_t getLength() override {
     71     return ItemEndOffsets.empty() ? 0 : ItemEndOffsets.back();
     72   }
     73 
     74 private:
     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 
     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