function F = fracF_cg(f, a)
%#codegen
%% fracF_cg Fractional Fourier Transform (FrFT) - codegen-ready version
%
%   Author: Canisio Barth
%
%   F = fracF_cg(f, a) computes the Fractional Fourier Transform (FrFT)
%   of the input signal 'f' for a single transform order 'a'.
%
%   This version is adapted for MATLAB Coder and hardware-oriented workflows.
%
%   Key characteristics:
%       - Fixed input size: [1024 x 1] complex(single)
%       - Output size: [512 x 1] complex(single)
%       - Assumes input 'f' is already interpolated externally
%       - No input validation (assumes valid scalar 'a' in core region)
%       - Deterministic execution (no branching, no dynamic allocation)
%
%   INPUTS:
%       f   - [1024 x 1] complex(single)
%       a   - scalar single
%
%   OUTPUTS:
%       F   - [512 x 1] complex(single)
%
%   Notes:
%       - Internal FFT size = 2048
%       - Designed for code generation and future FPGA mapping

% Fixed sizes
N    = 1024;
%N2   = 512;
Nfft = 2048;

% Ensure types
pi_s = single(pi);

% Transform parameter
phi = a * (pi_s / 2);

% Precompute trig terms
tan_half_phi = tan(phi / 2);
sin_phi = sin(phi);
cos_phi = cos(phi);

csc_phi = 1 / sin_phi;
cot_phi = cos_phi / sin_phi;

twoDelta = 2 * sqrt(single(N) / 2);

%% === Chirp A ===
n = single((-N/2:N/2-1).') / twoDelta;

Achirp = exp(-1j * pi_s * (n .* n) * tan_half_phi);

%% Chirp multiplication #1
g = Achirp .* f;

%% === Chirp B ===
m = single((-N:N-1).') / twoDelta;

Bchirp = exp(1j * pi_s * csc_phi .* (m .* m));

%% === Zero-padded buffer ===
g_pad = complex(zeros(Nfft,1,'single'));
g_pad(1:N) = g;

%% === FFT convolution ===
G = ifft( fft(g_pad) .* fft(Bchirp) );

%% Extract valid part and decimate
G_valid = G(N+1:2:end);   % [512 x 1]

%% Complex phase constant
Aphi = sqrt(1 - 1j * cot_phi);

%% === Chirp multiplication #2 ===
F = (Aphi / twoDelta) .* G_valid .* Achirp(1:2:end);

end