Cfft - Analog Devices VISUALDSP++ 3.5 Manual

DSP Run-Time Library Reference

cfft

N point complex input FFT
Synopsis
#include <filter.h>
void cfft_fr16(in[], t[], out[], w[], wst, n, block_exponent,
scale_method)
const complex_fract16 in[]
complex_fract16 t[];
complex_fract16 out[];
const complex_fract16 w[];
int wst;
int n;
int *block_exponent;
int scale method;
Description
This function transforms the time domain complex input signal sequence
to the frequency domain by using the radix-2 Fast Fourier Transform
(FFT).
The size of the input array
working buffer
The function does not impose any special memory alignment require-
ments on the arrays. However, benefits in run-time performance will be
realized if the output array is allocated on an address boundary that is a
multiple of twice the FFT size. If the input data can be overwritten, then
optimum memory usage can be achieved by specifying the input array as
either the output array or as the temporary array. Specifying the input
array as the temporary array will also result in increased run-time
performance.
4-36
/* input sequence
/* temporary working buffer
/* output sequence
/* twiddle sequence
/* twiddle factor stride
/* number of FFT points
/* block exponent of output data */
/* scaling method desired 0-none,
, the output array
in
is , where represents the number of points in the FFT.
t n n
VisualDSP++ 3.5 C/C++ Compiler and Library Manual
1-static, 2-dynamic
, and the temporary
out
for ADSP-219x DSPs
*/
*/
*/
*/
*/
*/
*/