On 05/31/10 14:30, Basile Starynkevitch wrote: [snip] > I would believe that replacing a complex function like above (which > contains a switch) with a virtual function call could probably be a win > in performance, not a loose. > > But perhaps my intuition is wrong. Honestly, I don't have exact figures > of the cost of virtual calls. IIRC, they have been costly for Intel > processors more than 5 years ago (but AMD processors perhaps run them > quicker at that time), but current Intel & AMD processors probably deal > better with indirect jump, so a virtual call is perhaps a with w.r.t. a > complex switch like above. [snip] The following post to the boost devel list:
http://sourceforge.net/mailarchive/message.php?msg_name=3f49a9f41003031715g19a23b94p47ccec2251acd55%40mail.gmail.com claims that switch statements are faster than virtual function calls. There's also this boost devel list post: http://lists.boost.org/Archives/boost/2008/01/132074.php where, instead of a virtual function table, a vector of function pointers is used. Using this method, I assume, would have a speed comparable to that of using a virtual function table since a virtual function table, IIUC, is essentially a vector of function pointers. However, that boost devel post claims using a switch statement would be faster. HTH. -regards, Larry
