void firdes_lowpass_f(float *output, int length, float cutoff_rate, window_t window)
{ //Generates symmetric windowed sinc FIR filter real taps
// length should be odd
// cutoff_rate is (cutoff frequency/sampling frequency)
//Explanation at Chapter 16 of dspguide.com
int middle=length/2;
float temp;
float (*window_function)(float) = firdes_get_window_kernel(window);
output[middle]=2*PI*cutoff_rate*window_function(0);
for(int i=1; i<=middle; i++) //@@firdes_lowpass_f: calculate taps
{
output[middle-i]=output[middle+i]=(sin(2*PI*cutoff_rate*i)/i)*window_function((float)i/middle);
//printf("%g %d %d %d %d | %g\n",output[middle-i],i,middle,middle+i,middle-i,sin(2*PI*cutoff_rate*i));
}
//Normalize filter kernel
float sum=0;
for(int i=0;i<length;i++) //@firdes_lowpass_f: normalize pass 1
{
sum+=output[i];
}
for(int i=0;i<length;i++) //@firdes_lowpass_f: normalize pass 2
{
output[i]/=sum;
}
}
static void init_sinc_table(rarch_sinc_resampler_t *resamp, double cutoff,
float *phase_table, int phases, int taps, bool calculate_delta)
{
int i, j;
double window_mod = window_function(0.0); /* Need to normalize w(0) to 1.0. */
int stride = calculate_delta ? 2 : 1;
double sidelobes = taps / 2.0;
for (i = 0; i < phases; i++)
{
for (j = 0; j < taps; j++)
{
double sinc_phase;
float val;
int n = j * phases + i;
double window_phase = (double)n / (phases * taps); /* [0, 1). */
window_phase = 2.0 * window_phase - 1.0; /* [-1, 1) */
sinc_phase = sidelobes * window_phase;
val = cutoff * sinc(M_PI * sinc_phase * cutoff) *
window_function(window_phase) / window_mod;
phase_table[i * stride * taps + j] = val;
}
}
if (calculate_delta)
{
int phase;
int p;
for (p = 0; p < phases - 1; p++)
{
for (j = 0; j < taps; j++)
{
float delta = phase_table[(p + 1) * stride * taps + j] -
phase_table[p * stride * taps + j];
phase_table[(p * stride + 1) * taps + j] = delta;
}
}
phase = phases - 1;
for (j = 0; j < taps; j++)
{
float val, delta;
double sinc_phase;
int n = j * phases + (phase + 1);
double window_phase = (double)n / (phases * taps); /* (0, 1]. */
window_phase = 2.0 * window_phase - 1.0; /* (-1, 1] */
sinc_phase = sidelobes * window_phase;
val = cutoff * sinc(M_PI * sinc_phase * cutoff) *
window_function(window_phase) / window_mod;
delta = (val - phase_table[phase * stride * taps + j]);
phase_table[(phase * stride + 1) * taps + j] = delta;
}
}
}
void apply_window_c(complexf* input, complexf* output, int size, window_t window)
{
float (*window_function)(float)=firdes_get_window_kernel(window);
for(int i=0;i<size;i++) //@apply_window_c
{
float rate=(float)i/(size-1);
iof(output,i)=iof(input,i)*window_function(2.0*rate+1.0);
qof(output,i)=qof(input,i)*window_function(2.0*rate+1.0);
}
}
void apply_window_f(float* input, float* output, int size, window_t window)
{
float (*window_function)(float)=firdes_get_window_kernel(window);
for(int i=0;i<size;i++) //@apply_window_f
{
float rate=(float)i/(size-1);
output[i]=input[i]*window_function(2.0*rate+1.0);
}
}
