Thanks Eric.
That's exactly the answer I was hoping for.

On Tue, 26 Aug 2008 18:02:14 -0700 (PDT), dim.raft@gmail.com wrote:

>Does that mean that the order O(   ) off the FFT algorithm is
>constant, and therefore the execution time depends only the execution
>speed of the particular mix of number arithmetic on the CPU?

The algorithm itself has no data dependence on the computations.   So
the same number of operations will be performed regardless of the
data.

Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.ericjacobsen.org

Blog: http://www.dsprelated.com/blogs-1/hf/Eric_Jacobsen.php

dim.raft@gmail.com wrote:
> I'm currently using the kiss FFT library in 32-bit fixed point mode in
> some software. I'm always using the same length FFT e.g. 1024-point.

> I want to know whether the average execution time of the FFT algorithm
> is likely to be dependent on the input signal waveform complexity.
> i.e. would you expect it to run faster for a purely DC signal, versus
> a complex arbitrary waveform?

How fast it runs depends on how fast the machine executes
floating point multiply and add.  Some machines can multiply
by zero faster than other numbers, others take the same time.

-- glen

Does that mean that the order O(   ) off the FFT algorithm is
constant, and therefore the execution time depends only the execution
speed of the particular mix of number arithmetic on the CPU?

I'm currently using the kiss FFT library in 32-bit fixed point mode in
some software. I'm always using the same length FFT e.g. 1024-point.

I want to know whether the average execution time of the FFT algorithm
is likely to be dependent on the input signal waveform complexity.
i.e. would you expect it to run faster for a purely DC signal, versus
a complex arbitrary waveform?

Thanks in advance.