I replaced everywhere the type of sizes with long long. This allows now opening of files larger than 2GB. It is really fast to open even a 4 GB file. With some hacks I made it possible to jump instantly to the end of a 4GB file. I will probably not give up, and will do some optimizations. There are some challenges:

1. line breaks are counted to often. This is not always needed. However do not know how much it costs to go through the 4GB and count the breaks.

2. When moving backwards, it seems that the full buffer is parsed from begin to the current position. This could be done backwards.