1 /*
2 * Copyright (c) 2010 The WebM project authors. All Rights Reserved.
3 *
4 * Use of this source code is governed by a BSD-style license
5 * that can be found in the LICENSE file in the root of the source
6 * tree. An additional intellectual property rights grant can be found
7 * in the file PATENTS. All contributing project authors may
8 * be found in the AUTHORS file in the root of the source tree.
9 */
10 #ifdef HAVE_CONFIG_H
11 #include "config.h"
12 #endif
13
14 #include "dboolhuff.h"
15
16 int
vp8dx_start_decode(BOOL_DECODER * br,const unsigned char * source,unsigned int source_sz,vp8_decrypt_cb * decrypt_cb,void * decrypt_state)17 vp8dx_start_decode (BOOL_DECODER * br,
18 const unsigned char *source,
19 unsigned int source_sz, vp8_decrypt_cb * decrypt_cb, void *decrypt_state)
20 {
21 br->user_buffer_end = source + source_sz;
22 br->user_buffer = source;
23 br->value = 0;
24 br->count = -8;
25 br->range = 255;
26 br->decrypt_cb = decrypt_cb;
27 br->decrypt_state = decrypt_state;
28
29 if (source_sz && !source)
30 return 1;
31
32 /* Populate the buffer */
33 vp8dx_bool_decoder_fill (br);
34
35 return 0;
36 }
37
38 void
vp8dx_bool_decoder_fill(BOOL_DECODER * br)39 vp8dx_bool_decoder_fill (BOOL_DECODER * br)
40 {
41 const unsigned char *bufptr = br->user_buffer;
42 VP8_BD_VALUE value = br->value;
43 int count = br->count;
44 int shift = VP8_BD_VALUE_SIZE - 8 - (count + 8);
45 size_t bytes_left = br->user_buffer_end - bufptr;
46 size_t bits_left = bytes_left * CHAR_BIT;
47 int x = (int) (shift + CHAR_BIT - bits_left);
48 int loop_end = 0;
49 unsigned char decrypted[sizeof (VP8_BD_VALUE) + 1];
50
51 if (br->decrypt_cb) {
52 size_t n =
53 bytes_left > sizeof (decrypted) ? sizeof (decrypted) : bytes_left;
54 br->decrypt_cb (br->decrypt_state, bufptr, decrypted, (int) n);
55 bufptr = decrypted;
56 }
57
58 if (x >= 0) {
59 count += VP8_LOTS_OF_BITS;
60 loop_end = x;
61 }
62
63 if (x < 0 || bits_left) {
64 while (shift >= loop_end) {
65 count += CHAR_BIT;
66 value |= (VP8_BD_VALUE) * bufptr << shift;
67 ++bufptr;
68 ++br->user_buffer;
69 shift -= CHAR_BIT;
70 }
71 }
72
73 br->value = value;
74 br->count = count;
75 }
76