107 lines
3.6 KiB
C++
107 lines
3.6 KiB
C++
//===- BinaryItemStream.h ---------------------------------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_SUPPORT_BINARYITEMSTREAM_H
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#define LLVM_SUPPORT_BINARYITEMSTREAM_H
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#include "llvm/ADT/ArrayRef.h"
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#include "llvm/Support/BinaryStream.h"
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#include "llvm/Support/BinaryStreamError.h"
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#include "llvm/Support/Error.h"
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#include <cstddef>
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#include <cstdint>
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namespace llvm {
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template <typename T> struct BinaryItemTraits {
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static size_t length(const T &Item) = delete;
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static ArrayRef<uint8_t> bytes(const T &Item) = delete;
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};
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/// BinaryItemStream represents a sequence of objects stored in some kind of
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/// external container but for which it is useful to view as a stream of
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/// contiguous bytes. An example of this might be if you have a collection of
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/// records and you serialize each one into a buffer, and store these serialized
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/// records in a container. The pointers themselves are not laid out
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/// contiguously in memory, but we may wish to read from or write to these
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/// records as if they were.
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template <typename T, typename Traits = BinaryItemTraits<T>>
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class BinaryItemStream : public BinaryStream {
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public:
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explicit BinaryItemStream(llvm::support::endianness Endian)
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: Endian(Endian) {}
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llvm::support::endianness getEndian() const override { return Endian; }
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Error readBytes(uint32_t Offset, uint32_t Size,
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ArrayRef<uint8_t> &Buffer) override {
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auto ExpectedIndex = translateOffsetIndex(Offset);
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if (!ExpectedIndex)
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return ExpectedIndex.takeError();
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const auto &Item = Items[*ExpectedIndex];
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if (auto EC = checkOffsetForRead(Offset, Size))
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return EC;
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if (Size > Traits::length(Item))
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return make_error<BinaryStreamError>(stream_error_code::stream_too_short);
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Buffer = Traits::bytes(Item).take_front(Size);
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return Error::success();
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}
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Error readLongestContiguousChunk(uint32_t Offset,
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ArrayRef<uint8_t> &Buffer) override {
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auto ExpectedIndex = translateOffsetIndex(Offset);
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if (!ExpectedIndex)
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return ExpectedIndex.takeError();
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Buffer = Traits::bytes(Items[*ExpectedIndex]);
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return Error::success();
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}
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void setItems(ArrayRef<T> ItemArray) {
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Items = ItemArray;
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computeItemOffsets();
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}
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uint32_t getLength() override {
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return ItemEndOffsets.empty() ? 0 : ItemEndOffsets.back();
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}
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private:
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void computeItemOffsets() {
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ItemEndOffsets.clear();
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ItemEndOffsets.reserve(Items.size());
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uint32_t CurrentOffset = 0;
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for (const auto &Item : Items) {
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uint32_t Len = Traits::length(Item);
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assert(Len > 0 && "no empty items");
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CurrentOffset += Len;
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ItemEndOffsets.push_back(CurrentOffset);
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}
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}
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Expected<uint32_t> translateOffsetIndex(uint32_t Offset) {
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// Make sure the offset is somewhere in our items array.
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if (Offset >= getLength())
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return make_error<BinaryStreamError>(stream_error_code::stream_too_short);
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++Offset;
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auto Iter = llvm::lower_bound(ItemEndOffsets, Offset);
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size_t Idx = std::distance(ItemEndOffsets.begin(), Iter);
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assert(Idx < Items.size() && "binary search for offset failed");
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return Idx;
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}
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llvm::support::endianness Endian;
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ArrayRef<T> Items;
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// Sorted vector of offsets to accelerate lookup.
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std::vector<uint32_t> ItemEndOffsets;
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};
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} // end namespace llvm
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#endif // LLVM_SUPPORT_BINARYITEMSTREAM_H
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