Method CopyFixedWidthValues

cpp/src/arrow/util/hashing.h:809–857

  }

  void CopyFixedWidthValues(int32_t start, int32_t width_size, int64_t out_size,
                            uint8_t* out_data) const {
    // This method exists to cope with the fact that the BinaryMemoTable does
    // not know the fixed width when inserting the null value. The data
    // buffer hold a zero length string for the null value (if found).
    //
    // Thus, the method will properly inject an empty value of the proper width
    // in the output buffer.
    //
    if (start >= size()) {
      return;
    }

    int32_t null_index = GetNull();
    if (null_index < start) {
      // Nothing to skip, proceed as usual.
      CopyValues(start, out_size, out_data);
      return;
    }

    builder_offset_type left_offset = binary_builder_.offset(start);

    // Ensure that the data length is exactly missing width_size bytes to fit
    // in the expected output (n_values * width_size).
#ifndef NDEBUG
    int64_t data_length = values_size() - static_cast<size_t>(left_offset);
    assert(data_length + width_size == out_size);
    ARROW_UNUSED(data_length);
#endif

    auto in_data = binary_builder_.value_data() + left_offset;
    // The null use 0-length in the data, slice the data in 2 and skip by
    // width_size in out_data. [part_1][width_size][part_2]
    auto null_data_offset = binary_builder_.offset(null_index);
    auto left_size = null_data_offset - left_offset;
    if (left_size > 0) {
      memcpy(out_data, in_data + left_offset, left_size);
    }
    // Zero-initialize the null entry
    memset(out_data + left_size, 0, width_size);

    auto right_size = values_size() - static_cast<size_t>(null_data_offset);
    if (right_size > 0) {
      // skip the null fixed size value.
      auto out_offset = left_size + width_size;
      assert(out_data + out_offset + right_size == out_data + out_size);
      memcpy(out_data + out_offset, in_data + null_data_offset, right_size);
    }
  }

  // Visit the stored values in insertion order.
  // The visitor function should have the signature `void(std::string_view)`