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/*−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−*/
/* Determine the magnitude od the number of points to be transformed.
/* Check whether we can use a radix4 decomposition or a mixed radix
/* transformation, by determining modulo 2.
/*−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−*/
for (i = 31, m = 1; (npoints & (1 << i)) == 0; i−−, m++) ;
radix
=
m & 1 ? 2 :
norm
=
m − 2;
/*−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−*/
/* The stride is quartered with every iteration of the outer loop. It
/* denotes the seperation between any two adjacent inputs to the butter */
/* −fly. This should start out at N/4, hence stride is initially set to */
/* N. For every stride, 6*stride twiddle factors are accessed. The
/* "tw_offset" is the offset within the current twiddle factor sub−
/* table. This is set to zero, at the start of the code and is used to
/* obtain the appropriate sub−table twiddle pointer by offsetting it
/* with the base pointer "ptr_w".
/*−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−*/
stride
=
npoints;
tw_offset
=
0;
fft_jmp
=
6 * stride;
while (stride > radix)
{
/*−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−*/
/* At the start of every iteration of the outer loop, "j" is set
/* to zero, as "w" is pointing to the correct location within the
/* twiddle factor array. For every iteration of the inner loop
/* 6 * stride twiddle factors are accessed. For eg,
/*
/* #Iteration of outer loop
/*
1
/*
2
/*
...
/*−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−*/
j
= 0;
fft_jmp >>= 2;
4;
# twiddle factors
6 N/4
6 N/16
DSP_fft16x16t
#times cycled
1
4
C64x+ DSPLIB Reference
*/
*/
*/
*/
*/
*/
*/
*/
*/
*/
*/
*/
*/
*/
*/
*/
*/
*/
4-109
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