CMSIS DSP Correlation

Hello,

I'm working on a real-time treatment using a correlation on ARM Cortex-M4 (kinetis k60), so the duration of the treatment is important for me.

So I tried several size of input parameters and  different functions to be as fast as possible.

But there is something I don't understand:

I tried arm_correlate_fast_q31 and arm_correlate_q31.

According to the documentation, the 'fast' function should be faster but less accurate ?

I measured the times and it seems the basic correlation is faster than the fast.

Example in my case:

arm_correlate_fast_q31(din0, 1024, din1, 1024, dout) > 367 ms

arm_correlate_q31(din0, 1024, din1, 1024, dout) >          272 ms

I use the last version of CMSIS (V1.4.5 b) and GCC.

Are there something I did wrong or that I misunderstood ?

Thank you,

Romain