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 #include "vp8/common/common.h"
14
vp8dx_start_decode(BOOL_DECODER * br,const unsigned char * source,unsigned int source_sz,vpx_decrypt_cb decrypt_cb,void * decrypt_state)15 int vp8dx_start_decode(BOOL_DECODER *br,
16 const unsigned char *source,
17 unsigned int source_sz,
18 vpx_decrypt_cb decrypt_cb,
19 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
vp8dx_bool_decoder_fill(BOOL_DECODER * br)38 void vp8dx_bool_decoder_fill(BOOL_DECODER *br)
39 {
40 const unsigned char *bufptr = br->user_buffer;
41 VP8_BD_VALUE value = br->value;
42 int count = br->count;
43 int shift = VP8_BD_VALUE_SIZE - CHAR_BIT - (count + CHAR_BIT);
44 size_t bytes_left = br->user_buffer_end - bufptr;
45 size_t bits_left = bytes_left * CHAR_BIT;
46 int x = (int)(shift + CHAR_BIT - bits_left);
47 int loop_end = 0;
48 unsigned char decrypted[sizeof(VP8_BD_VALUE) + 1];
49
50 if (br->decrypt_cb) {
51 size_t n = MIN(sizeof(decrypted), bytes_left);
52 br->decrypt_cb(br->decrypt_state, bufptr, decrypted, (int)n);
53 bufptr = decrypted;
54 }
55
56 if(x >= 0)
57 {
58 count += VP8_LOTS_OF_BITS;
59 loop_end = x;
60 }
61
62 if (x < 0 || bits_left)
63 {
64 while(shift >= loop_end)
65 {
66 count += CHAR_BIT;
67 value |= (VP8_BD_VALUE)*bufptr << shift;
68 ++bufptr;
69 ++br->user_buffer;
70 shift -= CHAR_BIT;
71 }
72 }
73
74 br->value = value;
75 br->count = count;
76 }
77