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 #include "dboolhuff.h"
12 #include "vp8/common/common.h"
13 #include "vpx_dsp/vpx_dsp_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, const unsigned char *source,
16 unsigned int source_sz, vpx_decrypt_cb decrypt_cb,
17 void *decrypt_state) {
18 br->user_buffer_end = source + source_sz;
19 br->user_buffer = source;
20 br->value = 0;
21 br->count = -8;
22 br->range = 255;
23 br->decrypt_cb = decrypt_cb;
24 br->decrypt_state = decrypt_state;
25
26 if (source_sz && !source) return 1;
27
28 /* Populate the buffer */
29 vp8dx_bool_decoder_fill(br);
30
31 return 0;
32 }
33
vp8dx_bool_decoder_fill(BOOL_DECODER * br)34 void vp8dx_bool_decoder_fill(BOOL_DECODER *br) {
35 const unsigned char *bufptr = br->user_buffer;
36 VP8_BD_VALUE value = br->value;
37 int count = br->count;
38 int shift = VP8_BD_VALUE_SIZE - CHAR_BIT - (count + CHAR_BIT);
39 size_t bytes_left = br->user_buffer_end - bufptr;
40 size_t bits_left = bytes_left * CHAR_BIT;
41 int x = shift + CHAR_BIT - (int)bits_left;
42 int loop_end = 0;
43 unsigned char decrypted[sizeof(VP8_BD_VALUE) + 1];
44
45 if (br->decrypt_cb) {
46 size_t n = VPXMIN(sizeof(decrypted), bytes_left);
47 br->decrypt_cb(br->decrypt_state, bufptr, decrypted, (int)n);
48 bufptr = decrypted;
49 }
50
51 if (x >= 0) {
52 count += VP8_LOTS_OF_BITS;
53 loop_end = x;
54 }
55
56 if (x < 0 || bits_left) {
57 while (shift >= loop_end) {
58 count += CHAR_BIT;
59 value |= (VP8_BD_VALUE)*bufptr << shift;
60 ++bufptr;
61 ++br->user_buffer;
62 shift -= CHAR_BIT;
63 }
64 }
65
66 br->value = value;
67 br->count = count;
68 }
69