HP Prime CAS & Large numbers

[parisse]

About 1K means that a multiprecision integer can currently not exceed 1K in storage. That's not much on the Prime, but you should not forget that the Prime is a child of the hp39gii and on the 39gii, 1K is not negligible.
As for global.cc, it's from the source code of Giac/Xcas.
For your other question, it's not my domain, I have no idea, you should perhaps start a new thread...