1 /*
2 libltc - en+decode linear timecode
3
4 Copyright (C) 2006-2012 Robin Gareus <robin@gareus.org>
5
6 This program is free software; you can redistribute it and/or modify
7 it under the terms of the GNU Lesser General Public License as
8 published by the Free Software Foundation, either version 3 of the
9 License, or (at your option) any later version.
10
11 This program is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public
17 License along with this library.
18 If not, see <http://www.gnu.org/licenses/>.
19 */
20
21 #include <stdio.h>
22 #include <stdlib.h>
23 #include <string.h>
24 #include <math.h>
25
26 #include "encoder.h"
27
28 /**
29 * add values to the output buffer
30 */
addvalues(LTCEncoder * e,int n)31 static int addvalues(LTCEncoder *e, int n) {
32 const ltcsnd_sample_t tgtval = e->state ? e->enc_hi : e->enc_lo;
33
34 if (e->offset + n >= e->bufsize) {
35 #if 0
36 fprintf(stderr, "libltc: buffer overflow: %d/%lu\n", (int) e->offset, (unsigned long) e->bufsize);
37 #endif
38 return 1;
39 }
40
41 ltcsnd_sample_t * const wave = &(e->buf[e->offset]);
42 const double tcf = e->filter_const;
43 if (tcf > 0) {
44 /* low-pass-filter
45 * LTC signal should have a rise time of 40 us +/- 10 us.
46 *
47 * rise-time means from <10% to >90% of the signal.
48 * in each call to addvalues() we start at 50%, so
49 * here we need half-of it. (0.000020 sec)
50 *
51 * e->cutoff = 1.0 -exp( -1.0 / (sample_rate * .000020 / exp(1.0)) );
52 */
53 int i;
54 ltcsnd_sample_t val = SAMPLE_CENTER;
55 int m = (n+1)>>1;
56 for (i = 0 ; i < m ; i++) {
57 val = val + tcf * (tgtval - val);
58 wave[n-i-1] = wave[i] = val;
59 }
60 } else {
61 /* perfect square wave */
62 memset(wave, tgtval, n);
63 }
64
65 e->offset += n;
66 return 0;
67 }
68
encode_byte(LTCEncoder * e,int byte,double speed)69 int encode_byte(LTCEncoder *e, int byte, double speed) {
70 if (byte < 0 || byte > 9) return -1;
71 if (speed ==0) return -1;
72
73 int err = 0;
74 const unsigned char c = ((unsigned char*)&e->f)[byte];
75 unsigned char b = (speed < 0)?128:1; // bit
76 const double spc = e->samples_per_clock * fabs(speed);
77 const double sph = e->samples_per_clock_2 * fabs(speed);
78
79 do
80 {
81 int n;
82 if ((c & b) == 0) {
83 n = (int)(spc + e->sample_remainder);
84 e->sample_remainder = spc + e->sample_remainder - n;
85 e->state = !e->state;
86 err |= addvalues(e, n);
87 } else {
88 n = (int)(sph + e->sample_remainder);
89 e->sample_remainder = sph + e->sample_remainder - n;
90 e->state = !e->state;
91 err |= addvalues(e, n);
92
93 n = (int)(sph + e->sample_remainder);
94 e->sample_remainder = sph + e->sample_remainder - n;
95 e->state = !e->state;
96 err |= addvalues(e, n);
97 }
98 /* this is based on the assumption that with every compiler
99 * ((unsigned char) 128)<<1 == ((unsigned char 1)>>1) == 0
100 */
101 if (speed < 0)
102 b >>= 1;
103 else
104 b <<= 1;
105 } while (b);
106
107 return err;
108 }
109