Code covered by the BSD License

### Mike Donovan (view profile)

These functions compute a fixed point radix-4 FFT.You can generate C code from this m-code.

```%#eml
% This is a radix-4 FFT, using decimation in frequency
% The input signal can be floating point or fixed point
% Works with real or complex input
% Modified for Embedded MATLAB support

% Initialize variables and signals
% NOTE: The length of the input signal should be a power of 4: 4, 16, 64, 256, etc.
N = length(s);
M = log2(N)/2;

% Initialize variables for floating or fixed point sim
if isfi(s)
NT = numerictype(s);
FM = fimath(s);
wl = NT.WordLength;
W=fi(exp(-1*2j*pi*(0:N-1)/N), 1, wl, wl - 2, FM);
S = fi(complex(zeros(size(s))), NT, FM);
R = fi(complex(zeros(size(s))), 1, wl, wl  - 1 - 2*M, FM);
sTemp = fi(complex(zeros(size(s))), NT, FM);
x = fi(complex(zeros(1,4)), NT, FM);
else
W=exp(-1*2j*pi*(0:N-1)/N);
S = complex(zeros(size(s)));
R = complex(zeros(size(s)));
sTemp = complex(zeros(size(s)));
x = complex(zeros(1,4));
end

% FFT algorithm
% Calculate butterflies for first M-1 stages
sTemp = s;
for stage = 0:M-2
for n=1:N/4
for m=1:4
x(m) = sTemp(n + (m-1)*N/4);
end
S((1:4)+(n-1)*4) = radix4bfly(x, floor((n-1)/(4^stage)) *(4^stage), 1, W);
end
sTemp = S;
end

% Calculate butterflies for last stage
for n=1:N/4
for m=1:4
x(m) = sTemp(n + (m-1)*N/4);
end
S((1:4)+(n-1)*4) = radix4bfly(x, floor((n-1)/(4^stage)) * (4^stage), 0, W);
end

% Rescale the final output
R(:) = S*N;

end

% For the last stage of a radix-4 FFT all the ABCD multiplers are 1.
% Use the stageFlag variable to indicate the last stage
% stageFlag = 0 indicates last FFT stage, set to 1 otherwise

% Initialize variables and scale by 1/4
if isfi(x)
a=bitshift(x(1),-2);b=bitshift(x(2),-2);c=bitshift(x(3),-2);d=bitshift(x(4),-2);
else
a=x(1)*.25;b=x(2)*.25;c=x(3)*.25;d=x(4)*.25;
end

A=a+b+c+d;
B=(a-b+c-d)*W(2*segment*stageFlag + 1);
C=(a-complex(-imag(b),real(b))-c+complex(-imag(d),real(d)))*W(segment*stageFlag + 1);
D=(a+complex(-imag(b),real(b))-c-complex(-imag(d),real(d)))*W(3*segment*stageFlag + 1);

Z = [A B C D];

end

```