ft8_lib/ft8/decode.h

#pragma once

#include <stdint.h>
#include <complex>

namespace ft8 {

struct MagArray {
	int num_blocks;	// number of total blocks (symbols)
	int num_bins;	// number of FFT bins
	int time_osr;	// number of time subdivisions
	int freq_osr;	// number of frequency subdivisions
	uint8_t * mag;	// FFT magnitudes as [blocks][time_sub][freq_sub][num_bins]
};

struct Candidate {
    int16_t      score;
    int16_t      time_offset;
    int16_t      freq_offset;
    uint8_t      time_sub;
    uint8_t      freq_sub;
};

class Monitor1Base {
public:
    Monitor1Base(float sample_rate, int time_osr = 2, int freq_osr = 2, float fmin = 300, float fmax = 3000);

    void feed(const float *frame);
    void search();
    void reset();
protected:
    float *window_fn;   // [nfft]
    float *fft_frame;   // [nfft]
    float *last_frame;  // [nfft * 3/4]
    std::complex<float> *freqdata; // [nfft/2 + 1]
    int nfft;

    int offset;
    int time_sub;
    ft8::MagArray power;

    // [N] real --> [N/2 + 1] log magnitudes (decibels)
    // virtual void fft_forward_mag_db(const float *frame, uint8_t *mag_db) = 0;
    virtual void fft_forward(const float *in, std::complex<float> *out) = 0;
};

// Localize top N candidates in frequency and time according to their sync strength (looking at Costas symbols)
// We treat and organize the candidate list as a min-heap (empty initially).
int find_sync(const MagArray * power, const uint8_t *sync_map, int num_candidates, Candidate *heap, int min_score = 0);


// Compute log likelihood log(p(1) / p(0)) of 174 message bits 
// for later use in soft-decision LDPC decoding
void extract_likelihood(const MagArray *power, const Candidate & cand, const uint8_t *code_map, float *log174);

}