Method GetZeroBasedValueOffsets

cpp/src/arrow/ipc/writer.cc:324–369

  template <typename ArrayType>
  Status GetZeroBasedValueOffsets(const ArrayType& array,
                                  std::shared_ptr<Buffer>* value_offsets) {
    // Share slicing logic between ListArray, BinaryArray and LargeBinaryArray
    using offset_type = typename ArrayType::offset_type;

    if (array.length() == 0) {
      *value_offsets = array.value_offsets();
      return Status::OK();
    }

    const int64_t required_bytes = sizeof(offset_type) * (array.length() + 1);

    offset_type first_offset = 0;
    RETURN_NOT_OK(MemoryManager::CopyBufferSliceToCPU(
        array.data()->buffers[1], array.offset() * sizeof(offset_type),
        sizeof(offset_type), reinterpret_cast<uint8_t*>(&first_offset)));

    if (first_offset > 0) {
      // If the offset of the first value is non-zero, then we must create a new
      // offsets buffer with shifted offsets.
      if (!array.data()->buffers[1]->is_cpu()) {
        return Status::NotImplemented("Rebasing non-CPU offsets");
      }
      ARROW_ASSIGN_OR_RAISE(auto shifted_offsets,
                            AllocateBuffer(required_bytes, options_.memory_pool));

      const offset_type* source_offsets = array.raw_value_offsets();
      auto dest_offsets = shifted_offsets->mutable_span_as<offset_type>();
      const offset_type start_offset = source_offsets[0];

      for (int i = 0; i <= array.length(); ++i) {
        dest_offsets[i] = source_offsets[i] - start_offset;
      }
      *value_offsets = std::move(shifted_offsets);
    } else {
      // ARROW-6046: if we have a truncated slice with unused leading or
      // trailing data, then we slice it.
      if (array.offset() > 0 || array.value_offsets()->size() > required_bytes) {
        *value_offsets = SliceBuffer(
            array.value_offsets(), array.offset() * sizeof(offset_type), required_bytes);
      } else {
        *value_offsets = array.value_offsets();
      }
    }
    return Status::OK();
  }

  template <typename ArrayType, typename offset_type = typename ArrayType::offset_type>
  Status GetZeroBasedListViewOffsets(const ArrayType& array,