Function SafeLoadWords

cpp/src/arrow/util/bitmap.h:427–447

  /// load words from bitmaps bitwise
  template <size_t N, typename Word>
  static void SafeLoadWords(const Bitmap (&bitmaps)[N], int64_t offset,
                            int64_t out_length, bool set_trailing_bits,
                            std::array<Word, N>* out) {
    out->fill(0);

    int64_t out_offset = set_trailing_bits ? sizeof(Word) * 8 - out_length : 0;

    Bitmap slices[N], out_bitmaps[N];
    for (size_t i = 0; i < N; ++i) {
      slices[i] = bitmaps[i].Slice(offset, out_length);
      out_bitmaps[i] = Bitmap(&out->at(i), out_offset, out_length);
    }

    int64_t bit_i = 0;
    Bitmap::VisitBits(slices, [&](std::bitset<N> bits) {
      for (size_t i = 0; i < N; ++i) {
        out_bitmaps[i].SetBitTo(bit_i, bits[i]);
      }
      ++bit_i;
    });
  }

  /// assert bitmaps have identical length and return that length
  static int64_t BitLength(const Bitmap* bitmaps, size_t N);