Analog Devices VISUALDSP++ 3.5 Manual page 453

The twiddle table is passed in the argument
twiddle factors. The function
n/2
tialize the array. If the twiddle table contains more factors than needed for
a particular call on
priately; otherwise it should be 1.
The argument
output to avoid overflow. If no scaling is selected by setting
to zero, then the input signal should be sufficiently conditioned to avoid
overflow. The
The function will perform static scaling if
static scaling, the function will scale intermediate results to prevent over-
flow. The final output will be scaled by 1/
set to
log2(n)
If
scale_method
Under dynamic scaling, the function will inspect the intermediate results
and will only scale to avoid overflow. Dynamic scaling therefore mini-
mizes loss of precision but at the possible cost of slightly reduced
performance. The
0 (which indicates that no scaling was performed) and
scaling was performed).
Algorithm
−
N 1
∑
=
X k ( ) x n W ( )
=
n 0
When the sequence length,
rithm is also available.
Domain
Input sequence length
VisualDSP++ 3.5 C/C++ Compiler and Library Manual
for ADSP-219x DSPs
, then the stride factor has to be set appro-
cfft_fr16
controls how the function should scale the
scale_method
argument will be set to zero.
block_exponent
.
is set to 2, then the function will select dynamic scaling.
block_exponent
n k
N
, equals power of four, the
n
must be a power of two and at least 16.
n
DSP Run-Time Library
, which must contain at least
w
twidfftrad2_fr16
scale_method
, and
n block_exponent
argument will be set to a value between
may be used to ini-
scale_method
is set to 1. For
will be
(as if static
log2(n)
algo-
cfftrad4
4-37