Function UnalignedBitmapOp

cpp/src/arrow/util/bitmap_ops.cc:382–404

template <template <typename> class BitOp>
void UnalignedBitmapOp(const uint8_t* left, int64_t left_offset, const uint8_t* right,
                       int64_t right_offset, uint8_t* out, int64_t out_offset,
                       int64_t length) {
  BitOp<uint64_t> op_word;
  BitOp<uint8_t> op_byte;

  auto left_reader = internal::BitmapWordReader<uint64_t>(left, left_offset, length);
  auto right_reader = internal::BitmapWordReader<uint64_t>(right, right_offset, length);
  auto writer = internal::BitmapWordWriter<uint64_t>(out, out_offset, length);

  auto nwords = left_reader.words();
  while (nwords--) {
    writer.PutNextWord(op_word(left_reader.NextWord(), right_reader.NextWord()));
  }
  auto nbytes = left_reader.trailing_bytes();
  while (nbytes--) {
    int left_valid_bits, right_valid_bits;
    uint8_t left_byte = left_reader.NextTrailingByte(left_valid_bits);
    uint8_t right_byte = right_reader.NextTrailingByte(right_valid_bits);
    DCHECK_EQ(left_valid_bits, right_valid_bits);
    writer.PutNextTrailingByte(op_byte(left_byte, right_byte), left_valid_bits);
  }
}

// XXX: The bits before left/right/out_offset, if unaligned, are untouched. But not for
// the bits after length. Caller should ensure proper alignment for the tail bits if