Hello!
The only possible reply her is: it depends.
What you can be sure of is that the FFT will consume nLogs
multiplication (therefore in your
case 256 log2(256) = 8x256 = 2048 multiplications.
Then, what you need to know:
- Is there a possibility of MAC operation (MAC = Multiply ACcumulate)?
- What number format are you using? Integer? Float? Double?
From this, the figures will change drastically. An example I know well: on a MSP430 (16 bit device),
an integer multiplication takes only a few clock cycles. One day, I have tried a float multiplication,
and it consumed about 300 cycles.
So it depends on your processor. If you have an FPU (e.g. STM43F429), then it will be light-fast.
If not, then it also depends on the CPU frequency, etc...
Dora.