Download Chapter 12 General and special-purpose digital signal processors

Chapter 12 General and special-purpose digital signal processors.
function cgdft
%
function cgdft compute DFT coefficients using DIT FFT algorithm
%
function cgfft.m is used to implement the constant geometry FFT
clear all;
direction = 1;
%1
- forward DFT, -1 - inverse DFT
in=fopen('datain.dat','r');
[x,count]=fscanf(in,'%g %g',[2 inf]);
fclose(in);
x = x(1,:)+x(2,:)*i;
% form complex numbers
npt = 2^(nextpow2(count/2)); % find the next power of two
x(1:npt) = [x; zeros(npt-count/2,1)]; % x is padded with trailing
zeros to npt
y=cgfft(x,npt,direction);
% calculate the constant geometry FFT
% Save/Print the results
out=fopen('dataout.dat','w');
fprintf(out,'%g %g\n',[real(y); imag(y)]);
fclose(out);
subplot(2,1,1),plot(1:npt,x); title('Input Signal');
subplot(2,1,2),plot(1:npt,y); title('Output Signal');
===============================================
function x=cgfft(x,npt,direction)
%
Function computes the DFT of a sequence using radix2 FFT
%
with constant geometry
% in-place bit reverse shuffling of data
j=2;
for n=2:npt
if n<j
t = x(j-1);
x(j-1) = x(n-1);
x(n-1) = t;
end
k = npt/2;
while k<j-1
j = j-k;
k = k/2;
end
j = j+k;
end
m = log2(npt); % calculate the number of stages: m=log2(npt)
w = exp(direction*2*pi*(0:npt/2-1)/npt*i); % pre-compute the twiddle
factors
% perform the FFT computation for each stage
for d=1:m
n = 1;
dk = 2^(d-1);
dr = npt/(2^d);
for k=0:dk-1
p = (k*npt)/(2^d)+1;
for r=1:dr
if rem(d,2)~=0
t = x(2*n)*conj(w(p));
x1(n) = x(2*n-1)+t;
x1(npt/2+n) = x(2*n-1)-t;
else
t = x1(2*n)*conj(w(p));
x(n) = x1(2*n-1)+t;
x(npt/2+n) = x1(2*n-1)-t;
end
n = n+1;
end
end
end
if rem(m,2)~=0
x = x1;
end
%If inverse fft is desired divide each coefficient by npt
if direction==-1
x = x /npt;
end