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#include <stdio.h>
#include <string.h>
#include <assert.h>
#include <stdlib.h>
#include <math.h>
#include "v17mod.h"
#define SAMPLE_RATE 8000
#define CARRIER_FREQ 1800
#define BAUD_RATE 2400
#define SYMBOL_INTERVAL ((float) SAMPLE_RATE/BAUD_RATE)
#define SINC_RADIUS 5
#define SYMBOLS_MAX 1024
static const float v17_7k2_x[] = {
0.6, -0.2, 0.6, -0.6,
-0.6, 0.2, -0.6, 0.6,
-0.2, 0.6, -0.2, 0.2,
0.2, -0.6, 0.2, -0.2
};
static const float v17_7k2_y[] = {
-0.6, 0.6, 0.2, -0.6,
0.6, -0.6, -0.2, 0.6,
0.2, -0.2, -0.6, 0.2,
-0.2, 0.2, 0.6, -0.2
};
void v17mod_init(struct v17mod_state *s) {
size_t l;
int i;
assert(s);
memset(s, 0, sizeof(*s));
s->xsymbols = malloc(l = (sizeof(float)*SYMBOLS_MAX));
s->ysymbols = malloc(l);
s->n_symbols = SINC_RADIUS*2;
for (i = 0; i < s->n_symbols; i++)
s->xsymbols[i] = s->ysymbols[i] = 0.0;
}
void v17mod_done(struct v17mod_state *s) {
assert(s);
free(s->xsymbols);
free(s->ysymbols);
}
static const float sinc_table[] = {
0.0000, -0.0000, -0.0002, -0.0005, -0.0009,
-0.0014, -0.0018, -0.0020, -0.0019, -0.0013,
0.0000, 0.0019, 0.0042, 0.0068, 0.0093,
0.0113, 0.0124, 0.0120, 0.0098, 0.0058,
-0.0000, -0.0073, -0.0153, -0.0234, -0.0303,
-0.0350, -0.0365, -0.0340, -0.0270, -0.0155,
0.0000, 0.0183, 0.0377, 0.0562, 0.0716,
0.0815, 0.0838, 0.0771, 0.0605, 0.0344,
-0.0000, -0.0403, -0.0832, -0.1243, -0.1589,
-0.1821, -0.1893, -0.1767, -0.1415, -0.0824,
0.0000, 0.1035, 0.2241, 0.3561, 0.4926,
0.6261, 0.7488, 0.8533, 0.9330, 0.9830,
1.0000, 0.9830, 0.9330, 0.8533, 0.7488,
0.6261, 0.4926, 0.3561, 0.2241, 0.1035,
0.0000, -0.0824, -0.1415, -0.1767, -0.1893,
-0.1821, -0.1589, -0.1243, -0.0832, -0.0403,
-0.0000, 0.0344, 0.0605, 0.0771, 0.0838,
0.0815, 0.0716, 0.0562, 0.0377, 0.0183,
0.0000, -0.0155, -0.0270, -0.0340, -0.0365,
-0.0350, -0.0303, -0.0234, -0.0153, -0.0073,
-0.0000, 0.0058, 0.0098, 0.0120, 0.0124,
0.0113, 0.0093, 0.0068, 0.0042, 0.0019,
0.0000, -0.0013, -0.0019, -0.0020, -0.0018,
-0.0014, -0.0009, -0.0005, -0.0002, -0.0000,
-0.0000
};
static float sinc(float x) {
int i;
assert(sizeof(sinc_table)/sizeof(float) == 121);
i = (int) (60+x*10+.5);
if (i < 0)
return 0;
if (i > 120)
return 0;
return sinc_table[i];
}
void v17mod_push(struct v17mod_state *s, const uint8_t *p, int l) {
int i, j;
assert(s && p && l);
assert(s->n_symbols+l <= SYMBOLS_MAX);
for (i = 0, j = (s->i_symbols+s->n_symbols) % SYMBOLS_MAX; i < l; i++, j = (j+1) % SYMBOLS_MAX) {
assert(p[i] < 16);
s->xsymbols[j] = v17_7k2_x[p[i]];
s->ysymbols[j] = v17_7k2_y[p[i]];
}
s->n_symbols += l;
}
inline static float symbol_at(struct v17mod_state *s, float *a, int i) {
int j = s->i_symbols+i;
assert(i >= 0);
assert(i < s->n_symbols);
while(j >= SYMBOLS_MAX)
j -= SYMBOLS_MAX;
assert(j>=0);
assert(j<SYMBOLS_MAX);
return a[j];
}
static float fsignal(struct v17mod_state *s, int i) {
float sum, d;
int n;
float *symbols;
assert(s && i >= 0 && i <= 1);
symbols = (i == 0) ? s->xsymbols : s->ysymbols;
sum = 0;
d = s->sample - s->symbol_index*SAMPLE_RATE/BAUD_RATE;
for (n = -SINC_RADIUS; n < SINC_RADIUS; n++) {
float a,b;
a = symbol_at(s, symbols, n+SINC_RADIUS);
b = sinc(-n + d*BAUD_RATE/SAMPLE_RATE);
sum += a*b;
}
assert(sum<=10);
assert(sum >=-10);
return sum;
}
int v17mod_pull(struct v17mod_state *s, float *p, int l) {
assert(s && p && l && p && l);
int n_samples = 0;
for (;;) {
float x;
int nsi;
if (s->sample % 800 == 0)
fprintf(stderr, "seconds: %i; samples: %i; symbols: %i \r", s->seconds, s->sample, s->symbol_index);
if (!l) {
fprintf(stderr, "v17_mod(): destination buffer too short\n");
return -1;
}
nsi = (int) ((float) s->sample*BAUD_RATE/SAMPLE_RATE);
if (nsi != s->symbol_index) {
s->i_symbols++;
s->n_symbols--;
while (s->i_symbols >= SYMBOLS_MAX)
s->i_symbols -= SYMBOLS_MAX;
s->symbol_index = nsi;
}
if (s->n_symbols < SINC_RADIUS*2)
return n_samples;
if (s->sample == SAMPLE_RATE) {
assert(s->symbol_index == BAUD_RATE);
s->symbol_index = s->sample = 0;
s->seconds++;
}
x = (s->sample % SAMPLE_RATE) * M_PI*2 * CARRIER_FREQ / SAMPLE_RATE;
*(p++) = fsignal(s, 0)*sin(x) + fsignal(s, 1)*cos(x);
l--;
s->sample++;
n_samples++;
}
}
#if (TEST == 3)
int main() {
fprintf(stderr, "%f\n", sinc(1.0/3));
return 0;
}
#endif
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