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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         549 : class BinaryItemStream : public BinaryStream {
      36             : public:
      37         403 :   explicit BinaryItemStream(llvm::support::endianness Endian)
      38         397 :       : Endian(Endian) {}
      39             : 
      40           0 :   llvm::support::endianness getEndian() const override { return Endian; }
      41             : 
      42          97 :   Error readBytes(uint32_t Offset, uint32_t Size,
      43             :                   ArrayRef<uint8_t> &Buffer) override {
      44          97 :     auto ExpectedIndex = translateOffsetIndex(Offset);
      45          97 :     if (!ExpectedIndex)
      46             :       return ExpectedIndex.takeError();
      47          97 :     const auto &Item = Items[*ExpectedIndex];
      48         194 :     if (auto EC = checkOffsetForRead(Offset, Size))
      49             :       return EC;
      50         194 :     if (Size > Traits::length(Item))
      51           0 :       return make_error<BinaryStreamError>(stream_error_code::stream_too_short);
      52          97 :     Buffer = Traits::bytes(Item).take_front(Size);
      53             :     return Error::success();
      54             :   }
      55             : 
      56        1277 :   Error readLongestContiguousChunk(uint32_t Offset,
      57             :                                    ArrayRef<uint8_t> &Buffer) override {
      58        1277 :     auto ExpectedIndex = translateOffsetIndex(Offset);
      59        1277 :     if (!ExpectedIndex)
      60             :       return ExpectedIndex.takeError();
      61        2554 :     Buffer = Traits::bytes(Items[*ExpectedIndex]);
      62             :     return Error::success();
      63             :   }
      64             : 
      65             :   void setItems(ArrayRef<T> ItemArray) {
      66         403 :     Items = ItemArray;
      67         403 :     computeItemOffsets();
      68             :   }
      69             : 
      70        1968 :   uint32_t getLength() override {
      71        1971 :     return ItemEndOffsets.empty() ? 0 : ItemEndOffsets.back();
      72             :   }
      73             : 
      74             : private:
      75         403 :   void computeItemOffsets() {
      76         403 :     ItemEndOffsets.clear();
      77         403 :     ItemEndOffsets.reserve(Items.size());
      78         403 :     uint32_t CurrentOffset = 0;
      79        1751 :     for (const auto &Item : Items) {
      80        1348 :       uint32_t Len = Traits::length(Item);
      81             :       assert(Len > 0 && "no empty items");
      82        1348 :       CurrentOffset += Len;
      83        1348 :       ItemEndOffsets.push_back(CurrentOffset);
      84             :     }
      85         403 :   }
      86             : 
      87        1374 :   Expected<uint32_t> translateOffsetIndex(uint32_t Offset) {
      88             :     // Make sure the offset is somewhere in our items array.
      89        1374 :     if (Offset >= getLength())
      90           0 :       return make_error<BinaryStreamError>(stream_error_code::stream_too_short);
      91        1374 :     ++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