include/llvm/Support/BinaryItemStream.h

   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(uint32_t Offset, uint32_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(uint32_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   uint32_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     uint32_t CurrentOffset = 0;
  78     for (const auto &Item : Items) {
  79       uint32_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(uint32_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 =
  92         std::lower_bound(ItemEndOffsets.begin(), ItemEndOffsets.end(), Offset);
  93     size_t Idx = std::distance(ItemEndOffsets.begin(), Iter);
  94     assert(Idx < Items.size() && "binary search for offset failed");
  95     return Idx;
  96   }
  97
  98   llvm::support::endianness Endian;
  99   ArrayRef<T> Items;
 100
 101   // Sorted vector of offsets to accelerate lookup.
 102   std::vector<uint32_t> ItemEndOffsets;
 103 };
 104
 105 } // end namespace llvm
 106
 107 #endif // LLVM_SUPPORT_BINARYITEMSTREAM_H