RtlAppendStringToString

NTSTATUS __stdcall RtlAppendStringToString(_STRING *Destination, const _STRING *Source){
  int Length; 
  __int64 v4; 

  Length = Source->Length;
  if( !(_WORD)Length )
    return 0;
  v4 = Destination->Length;
  if( (int)v4 + Length <= (unsigned int)Destination->MaximumLength )
  {
    memmove(&Destination->Buffer[v4], Source->Buffer, Source->Length);
    Destination->Length += Length;
    return 0;
  }
  return -1073741789;
}

Referenced by: