Analog Devices VISUALDSP++ 3.5 Manual page 455

The twiddle table is passed in the argument
¾ twiddle coefficients. The function
n
initialize the array. If the twiddle table contains more coefficients than
needed for a particular call on
be set appropriately; otherwise it should be one.
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
argument will be set to
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,
must be used. See
Domain
Input sequence length
VisualDSP++ 3.5 C/C++ Compiler and Library Manual
for ADSP-219x DSPs
cfftrad4_fr16
controls how the function should scale the
scale_method
argument will be set to zero.
block_exponent
.
log2(n)
is set to 2, then the function will select dynamic scaling.
block_exponent
nk
N
, is not a power of four, the radix2 method
n
"cfft" on page 4-36
must be a power of four, and at least 16.
n
DSP Run-Time Library
, which must contain at least
w
twidfftrad4_fr16
, then the stride factor has to
scale_method
, and
1/n block_exponent
argument will be set to a value between
for more information.
may be used to
scale_method
is set to 1. For
(as if static
log2(n)
4-39