Timings on my machine (2.67ghz Xeon W3520): $time ./c_compiled_with_O2 1000000 real 0m0.362s user 0m0.360s $time ./c_compiled_with_O3 1000000

Timings on my machine (2.67ghz Xeon W3520): $time ./c_compiled_with_O2 1000000 real 0m0.362s user 0m0.360s $time ./c_compiled_with_O3 1000000 real 0m0.189s user 0m0.184s I also tried dropping all the cdefs from the Cython code and running the Python version in Parakeet (http://www.parakeetpython.com http://www.parakeetpython.com) and it took 0.57s (whereas CPython without the @jit decorator took 19.57s).