Function LoadPartialWord

cpp/src/arrow/util/bit_run_reader.h:305–322

  }

  uint64_t LoadPartialWord(int8_t bit_offset, int64_t num_bits) {
    assert(num_bits > 0);
    uint64_t word = 0;
    const int64_t num_bytes = bit_util::BytesForBits(num_bits);
    if (Reverse) {
      // Read in the most significant bytes of the word
      bitmap_ -= num_bytes;
      memcpy(reinterpret_cast<char*>(&word) + 8 - num_bytes, bitmap_, num_bytes);
      // XXX MostSignificantBitmask
      return (bit_util::ToLittleEndian(word) << bit_offset) &
             ~bit_util::LeastSignificantBitMask<uint64_t>(64 - num_bits);
    } else {
      memcpy(&word, bitmap_, num_bytes);
      bitmap_ += num_bytes;
      return (bit_util::ToLittleEndian(word) >> bit_offset) &
             bit_util::LeastSignificantBitMask<uint64_t>(num_bits);
    }
  }

  void SkipNextZeros() {
    assert(current_num_bits_ == 0);