Martin Ettl wrote: > Hello friends, > > i have made tests using the fma()-function and discovered an issue (see also this thread: http://gcc.gnu.org/ml/gcc-help/2009-04/msg00121.html). Brian Budge sent me a short benchmark programm to measure the execution time on my machine. Finally the fma() operation was faster than the a*b+c operation, but: > > If you use the -ansi flag to compile, then the fma()-operation takes 4-5-times longer, as without. > > So, now my question: Is this a known issue or an intendet behaviour? If yes, what other flags slow down such functions? Has anybody experienced a similiar case? fma() is new for C99. In gcc, -ansi means C89, the old standard. So, when you say -ansi the fast fma() builtin is disabled, and a C library call is used instead. You're seeing the effect of disabling gcc builtin ofr fma(). Andrew.
