Hey Bruno, On 01.06.2011 16:48, Bruno Bresciani wrote: The function checks if, for a given transaction T and a bitfield of callbacks, any of the callbacks are registered for T. It does so my logically ANDing the transaction bitfield (which represents the set of registered callbacks) with the bitfield of callbacks you would like to be checked. For each callback actually registered, the corresponding pair of bits will yield one w.r.t. to the AND operation. Therefore, if at least one of the given callbacks is registered, the entire AND operation will result in a value greater zero, thereby indicating that the transaction does have at least one of the given callbacks registered. For instance, if the bitfield of registered callbacks for T is 1011, and it is to be checked whether the callback bitfield 0110 matches, the outcome of 1011 & 0110 = 0010 > 0, meaning that at least one of the given callbacks is registered (which, in this example, happens to be the second transaction callback defined in t_hooks.h). HTH, --Timo