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#include <assert.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include <stdio.h>
#include "interpol.h"
#include "util.h"
void interpol_init(struct interpol_state *s, int frac, int radius) {
int l;
assert(s && frac);
memset(s, 0, sizeof(struct interpol_state));
s->frac = frac;
s->radius = radius;
s->coeff = malloc((l = s->radius*frac)*sizeof(float));
s->coeff_valid = malloc(l*sizeof(int));
assert(s->coeff_valid && s->coeff);
memset(s->coeff_valid, 0, l*sizeof(int));
}
void interpol_done(struct interpol_state *s) {
assert(s);
free(s->coeff);
free(s->coeff_valid);
}
static float sinc(struct interpol_state *s, int x) {
assert(s);
if (x == 0)
return 1;
if (x < 0)
x = -x;
if (x >= s->frac * s->radius)
return 0;
if (!s->coeff_valid[x]) {
float fx = ((float) x)/s->frac;
float hanning = .5*(1+cos(M_PI * fx / s->radius));
float _sinc = sin(M_PI * fx) / M_PI / fx;
/*fprintf(stderr, "%2.10f %2.10f %2.10f\n", fx, hanning, _sinc);*/
assert(_sinc <= 1);
assert(_sinc >= -1);
assert(hanning >= 0);
assert(hanning <= 1);
s->coeff[x] = hanning * _sinc;
s->coeff_valid[x] = 1;
}
return s->coeff[x];
}
float interpol_get(struct interpol_state *s, float *p, int l, float x) {
int i, j, z, d, n;
float sum;
assert(s && p && l);
i = (int) roundf(x*s->frac); /* x in units of 1/fracs */
z = i/s->frac; /* index of sample left of x */
j = z*s->frac; /* index of sample left of x in units of 1/fracs */
d = i-j;
sum = 0;
for (n = -s->radius; n <= s->radius; n++) {
int k = z + n; /* sample of current sinc pulse */
if (k < 0 || k >= l)
fprintf(stderr, "interpol.c: index out of bound: %i not in 0...%i\n", k, l);
else {
/*
char txt[2];
snprintf(txt, sizeof(txt), "%f", p[k]);
fprintf(stderr, "%i %i\r", k, l);
*/
sum += p[k] * sinc(s, -n*s->frac + d);
}
}
return sum;
}
#if (TEST == 5)
int main() {
struct interpol_state s;
int x;
int frac = 9;
interpol_init(&s, frac);
for (x = -10*frac; x <= 10*frac; x ++) {
fprintf(stderr, "%2.5f -> %2.5f\n", (float)x/frac, sinc(&s, x));
}
interpol_done(&s);
return 0;
}
#endif
#if (TEST == 6)
int main() {
struct interpol_state s;
float buf[1024], x;
int i, frac = 37;
interpol_init(&s, frac);
for (i = 0; i < 1024; i++)
buf[i] = 1;
for (x = 0; x < 1024; x += 0.1) {
float y = interpol_get(&s, buf, 1024, x);
//loop_write(1, &y, sizeof(float));
fprintf(stderr, "%2.10f => %2.10f\n", x, y);
}
interpol_done(&s);
return 0;
}
#endif
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