Some articles on efun, efuns:

LPUniversity Foundation - Basic Structure - Function Types
... efun An efun, or "external function", is defined by the driver ... Efuns are written in C and compiled statically into the driver, so they generally run much faster than other function types, but are more difficult to ... all functions written in LPC, so, for example, the efun this_player can be called with the syntax this_player, or efunthis_player if one needs to ...