Translating matlab's AGC function to C

Question

I am trying to translate the Automatic Gain Control block from Matlab's communications toolbox. Here is the documentation but the relevant parts are summarized below:

The block diagram

Where

And

This is the code I've written:

double AGC_Detector(int N, float complex* input, int ndx)
{
   double samp = 0;
   for(int i = ndx*N; i < (ndx+1)*(N-1); i++)
   {
       samp += cabs(input[i])*cabs(input[i]);
   }
   samp = samp/N;
   return samp;
}

void use_AGC(float complex* input, 
             float complex* output, 
             double step, 
             double desired_pwr, 
             int avrg_len, 
             int max_pwr, 
             int len)
{
   double z = 0;
   double e = 0;
   double g = 0;
   double prev_g = 0;
   double dtctr = 0;

   for(int i = 0; i < len; i++)
   {
       dtctr = AGC_Detector(avrg_len,input,i);
       z = dtctr * exp(2*prev_g);
       e = desired_pwr - log(z);
       g = prev_g + step*e;
       if(g > max_pwr)
       {
           g = max_pwr;
       }
       prev_g = g;
       output[i] = input[i] * exp(prev_g);
   }
}

But I am not getting the same output I get for the same values in Matlab. What am I doing wrong?

Thank You!

Answer 1

I figured it out. Code below gives same output as matlab for a given set of complex data.

double AGC_Detector(double complex input, double* sum, double state[], unsigned int* idx, int N)
{
    unsigned int first;
    unsigned int nth;
    double output;
    double val = cabs(input)*cabs(input);
    *sum += val;
    output = (*sum)*(1.0/N);
    *sum -= state[*idx-1];

    if(*sum < 0.0){*sum = 0.0;}

    state[*idx-1] = val;
    first = *idx;
    nth = first + 1;

    if(nth < first){nth = 0xFFFFFFFF;}

    *idx = nth;

    if(*idx > N-1){*idx = 1;}

    return output;
}


void use_AGC(double complex* input, double complex* output, double step, double desired_pwr, int avrg_len, int max_pwr, int len)
{
    unsigned int idx = 1;
    int filt_len = avrg_len-1;
    double K = step;
    double g = 0;
    double sum = 0;
    double dtctr = 0;
    double filterState[filt_len];

    for(int i = 0; i < filt_len; i++){filterState[i] = 0;}

    for(int i = 0; i < avrg_len; i++)
    {
        dtctr = AGC_Detector(input[i], &sum, filterState, &idx, avrg_len);
        output[i] = input[i] * exp(g);
        dtctr = log(dtctr);
        g += K*(desired_pwr - (dtctr + 2.0*g));
        if(g > max_pwr){g = max_pwr;}
    }
}