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
11
12 #include "dboolhuff.h"
13
vp8dx_start_decode(BOOL_DECODER * br,const unsigned char * source,unsigned int source_sz,vp8_decrypt_cb * decrypt_cb,void * decrypt_state)14 int vp8dx_start_decode(BOOL_DECODER *br,
15 const unsigned char *source,
16 unsigned int source_sz,
17 vp8_decrypt_cb *decrypt_cb,
18 void *decrypt_state)
19 {
20 br->user_buffer_end = source+source_sz;
21 br->user_buffer = source;
22 br->value = 0;
23 br->count = -8;
24 br->range = 255;
25 br->decrypt_cb = decrypt_cb;
26 br->decrypt_state = decrypt_state;
27
28 if (source_sz && !source)
29 return 1;
30
31 /* Populate the buffer */
32 vp8dx_bool_decoder_fill(br);
33
34 return 0;
35 }
36
vp8dx_bool_decoder_fill(BOOL_DECODER * br)37 void vp8dx_bool_decoder_fill(BOOL_DECODER *br)
38 {
39 const unsigned char *bufptr = br->user_buffer;
40 VP8_BD_VALUE value = br->value;
41 int count = br->count;
42 int shift = VP8_BD_VALUE_SIZE - 8 - (count + 8);
43 size_t bytes_left = br->user_buffer_end - bufptr;
44 size_t bits_left = bytes_left * CHAR_BIT;
45 int x = (int)(shift + CHAR_BIT - bits_left);
46 int loop_end = 0;
47 unsigned char decrypted[sizeof(VP8_BD_VALUE) + 1];
48
49 if (br->decrypt_cb) {
50 size_t n = bytes_left > sizeof(decrypted) ? sizeof(decrypted) : bytes_left;
51 br->decrypt_cb(br->decrypt_state, bufptr, decrypted, (int)n);
52 bufptr = decrypted;
53 }
54
55 if(x >= 0)
56 {
57 count += VP8_LOTS_OF_BITS;
58 loop_end = x;
59 }
60
61 if (x < 0 || bits_left)
62 {
63 while(shift >= loop_end)
64 {
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