On 20 December 2011 10:20, Ico wrote: > > Still, I'm not sure if sse is part of the problem and/or solution. It's the solution. > I have been reducing the program to see what the smallest code is that still > shows this behaviour. Latest version is below. > > > $ gcc -msse -mfpmath=sse -O3 -march=native test.c What is "native" for your system, i686? (also, what does gcc -dumpmachine show?) i686 doesn't support SSE, you need at least pentium3. Remove the -msse and see if you get a warning telling you SSE instructions are disabled. Try -march=pentium3 -mfpmath=sse instead (without -msse) If you don't have at least a pentium3, you're stuck with the 387 FP registers, and have to use horrible code. > $ time ./a.out 0.9 > > real 0m2.653s > user 0m2.648s > sys 0m0.002s That looks as though you're still not using SSE registers. > $ time ./a.out 0.001 > > real 0m0.144s > user 0m0.140s > sys 0m0.002s
