Function CopyEndChars

cpp/src/arrow/csv/writer.cc:70–79

This function is to improve performance. It copies CSV delimiter and eol without calling `memcpy`. Each CSV field is followed by a delimiter or eol, which is often only one or two chars. If copying both the field and delimiter with `memcpy`, CPU may suffer from high branch misprediction as we are tripping `memcpy` with interleaved (normal/tiny/normal/tiny/...) buffer sizes, which are handled separ

// separately inside `memcpy`. This function goes fast path if the buffer
// size is one or two chars to leave `memcpy` only for copying CSV fields.
void CopyEndChars(char* dest, const char* src, size_t size) {
  if (size == 1) {
    // for fixed size memcpy, compiler will generate direct load/store opcode
    memcpy(dest, src, 1);
  } else if (size == 2) {
    memcpy(dest, src, 2);
  } else {
    memcpy(dest, src, size);
  }
}

struct SliceIteratorFunctor {
  Result<std::shared_ptr<RecordBatch>> Next() {