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/*
libltc - en+decode linear timecode
Copyright (C) 2006-2012 Robin Gareus <robin@gareus.org>
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation, either version 3 of the
License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library.
If not, see <http://www.gnu.org/licenses/>.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include "ltc/encoder.h"
/**
* add values to the output buffer
*/
static int addvalues(LTCEncoder *e, int n) {
const ltcsnd_sample_t tgtval = e->state ? e->enc_hi : e->enc_lo;
if (e->offset + n >= e->bufsize) {
#if 0
fprintf(stderr, "libltc: buffer overflow: %d/%lu\n", (int) e->offset, (unsigned long) e->bufsize);
#endif
return 1;
}
ltcsnd_sample_t * const wave = &(e->buf[e->offset]);
const double tcf = e->filter_const;
if (tcf > 0) {
/* low-pass-filter
* LTC signal should have a rise time of 40 us +/- 10 us.
*
* rise-time means from <10% to >90% of the signal.
* in each call to addvalues() we start at 50%, so
* here we need half-of it. (0.000020 sec)
*
* e->cutoff = 1.0 -exp( -1.0 / (sample_rate * .000020 / exp(1.0)) );
*/
int i;
ltcsnd_sample_t val = SAMPLE_CENTER;
int m = (n+1)>>1;
for (i = 0 ; i < m ; i++) {
val = val + tcf * (tgtval - val);
wave[n-i-1] = wave[i] = val;
}
} else {
/* perfect square wave */
memset(wave, tgtval, n);
}
e->offset += n;
return 0;
}
int encode_byte(LTCEncoder *e, int byte, double speed) {
if (byte < 0 || byte > 9) return -1;
if (speed ==0) return -1;
int err = 0;
const unsigned char c = ((unsigned char*)&e->f)[byte];
unsigned char b = (speed < 0)?128:1; // bit
const double spc = e->samples_per_clock * fabs(speed);
const double sph = e->samples_per_clock_2 * fabs(speed);
do
{
int n;
if ((c & b) == 0) {
n = (int)(spc + e->sample_remainder);
e->sample_remainder = spc + e->sample_remainder - n;
e->state = !e->state;
err |= addvalues(e, n);
} else {
n = (int)(sph + e->sample_remainder);
e->sample_remainder = sph + e->sample_remainder - n;
e->state = !e->state;
err |= addvalues(e, n);
n = (int)(sph + e->sample_remainder);
e->sample_remainder = sph + e->sample_remainder - n;
e->state = !e->state;
err |= addvalues(e, n);
}
/* this is based on the assumption that with every compiler
* ((unsigned char) 128)<<1 == ((unsigned char 1)>>1) == 0
*/
if (speed < 0)
b >>= 1;
else
b <<= 1;
} while (b);
return err;
}
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