Strange results for MOD in CAS

[parisse]

MOD is not a synonym of mod in CAS.

If xcas_mode()==0, mod will build an element of Z/nZ, like 27 mod 5 -> 2 %% 5.
If xcas_mode()>0, mod will call irem and return an element of Z; 27 mod 5 -> 2
The difference will become clear if you make further operations on the result, e.g. multiply by 3.
It's unclear for me how xcas_mode can be modified on the Prime...

MOD in CAS will call _MODULO in rpn.cc, it's not the same code as irem, I don't remember the difference, probably _MODULO behaves more like MOD in HOME.