1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
|
/* Copyright (C) 2005 Ole André Vadla Ravnås <[email protected]>
*
* This library 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 2.1 of the License, or (at your option) any later version.
*
* This library 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, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <stdlib.h>
#include "mimic-private.h"
extern guchar _col_zag[64];
extern VlcSymbol _vlc_alphabet[16][128];
/*
* _vlc_encode_block
*
* Serialize an 8x8 block using variable length coding.
*/
void _vlc_encode_block(MimCtx *ctx, const gint *block, gint num_coeffs)
{
gint i, num_zeroes;
/* The DC value is written out as is. */
_write_bits(ctx, block[0], 8);
/* Number of zeroes prefixing the next non-zero value. */
num_zeroes = 0;
for (i = 1; i < num_coeffs && num_zeroes <= 14; i++) {
/* Fetch AC coefficients from block in zig-zag order. */
gint value = block[_col_zag[i]];
if (value != 0) {
VlcSymbol sym;
/* Clip input values to [-128, +128]. */
if (value < -128)
value = -128;
else if (value > 128)
value = 128;
/* Look up symbol for the current non-zero value. */
sym = _vlc_alphabet[num_zeroes][abs(value) - 1];
/* No symbol? very rare... */
if (sym.length1 <= 0)
break;
/* The symbols for negative values are the same as for positives, minus one. */
if (value < 0) {
if (sym.length2 > 0)
sym.part2 -= 1;
else
sym.part1 -= 1;
}
/* Write out the full symbol. */
_write_bits(ctx, sym.part1, sym.length1);
if (sym.length2 > 0)
_write_bits(ctx, sym.part2, sym.length2);
/* Start counting zeroes again. */
num_zeroes = 0;
} else {
num_zeroes++;
}
}
/* Write out EOB if necessary. */
if (num_zeroes > 0)
_write_bits(ctx, 0xA, 4);
}
|
