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  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::support::endianness Endian)
  37.       : Endian(Endian) {}
  38.  
  39.   llvm::support::endianness getEndian() const override { return Endian; }
  40.  
  41.   Error readBytes(uint64_t Offset, uint64_t Size,
  42.                   ArrayRef<uint8_t> &Buffer) override {
  43.     auto ExpectedIndex = translateOffsetIndex(Offset);
  44.     if (!ExpectedIndex)
  45.       return ExpectedIndex.takeError();
  46.     const auto &Item = Items[*ExpectedIndex];
  47.     if (auto EC = checkOffsetForRead(Offset, Size))
  48.       return EC;
  49.     if (Size > Traits::length(Item))
  50.       return make_error<BinaryStreamError>(stream_error_code::stream_too_short);
  51.     Buffer = Traits::bytes(Item).take_front(Size);
  52.     return Error::success();
  53.   }
  54.  
  55.   Error readLongestContiguousChunk(uint64_t Offset,
  56.                                    ArrayRef<uint8_t> &Buffer) override {
  57.     auto ExpectedIndex = translateOffsetIndex(Offset);
  58.     if (!ExpectedIndex)
  59.       return ExpectedIndex.takeError();
  60.     Buffer = Traits::bytes(Items[*ExpectedIndex]);
  61.     return Error::success();
  62.   }
  63.  
  64.   void setItems(ArrayRef<T> ItemArray) {
  65.     Items = ItemArray;
  66.     computeItemOffsets();
  67.   }
  68.  
  69.   uint64_t getLength() override {
  70.     return ItemEndOffsets.empty() ? 0 : ItemEndOffsets.back();
  71.   }
  72.  
  73. private:
  74.   void computeItemOffsets() {
  75.     ItemEndOffsets.clear();
  76.     ItemEndOffsets.reserve(Items.size());
  77.     uint64_t CurrentOffset = 0;
  78.     for (const auto &Item : Items) {
  79.       uint64_t Len = Traits::length(Item);
  80.       assert(Len > 0 && "no empty items");
  81.       CurrentOffset += Len;
  82.       ItemEndOffsets.push_back(CurrentOffset);
  83.     }
  84.   }
  85.  
  86.   Expected<uint32_t> translateOffsetIndex(uint64_t Offset) {
  87.     // Make sure the offset is somewhere in our items array.
  88.     if (Offset >= getLength())
  89.       return make_error<BinaryStreamError>(stream_error_code::stream_too_short);
  90.     ++Offset;
  91.     auto Iter = llvm::lower_bound(ItemEndOffsets, Offset);
  92.     size_t Idx = std::distance(ItemEndOffsets.begin(), Iter);
  93.     assert(Idx < Items.size() && "binary search for offset failed");
  94.     return Idx;
  95.   }
  96.  
  97.   llvm::support::endianness Endian;
  98.   ArrayRef<T> Items;
  99.  
  100.   // Sorted vector of offsets to accelerate lookup.
  101.   std::vector<uint64_t> ItemEndOffsets;
  102. };
  103.  
  104. } // end namespace llvm
  105.  
  106. #endif // LLVM_SUPPORT_BINARYITEMSTREAM_H
  107.