Method operator()

cpp/src/arrow/io/memory_test.cc:458–477

A transform that swaps every pair of bytes

struct SwappingTransform {
  // A transform that swaps every pair of bytes
  Result<std::shared_ptr<Buffer>> operator()(const std::shared_ptr<Buffer>& buf) {
    int64_t dest_size = bit_util::RoundDown(buf->size() + has_pending_, 2);
    ARROW_ASSIGN_OR_RAISE(auto dest, AllocateBuffer(dest_size));
    const uint8_t* data = buf->data();
    uint8_t* out_data = dest->mutable_data();
    if (has_pending_ && dest_size > 0) {
      *out_data++ = *data++;
      *out_data++ = pending_byte_;
      dest_size -= 2;
    }
    for (int64_t i = 0; i < dest_size; i += 2) {
      out_data[i] = data[i + 1];
      out_data[i + 1] = data[i];
    }
    has_pending_ = has_pending_ ^ (buf->size() & 1);
    if (has_pending_) {
      pending_byte_ = buf->data()[buf->size() - 1];
    }
    return std::shared_ptr<Buffer>(std::move(dest));
  }

 protected:
  bool has_pending_ = 0;