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 if (source_sz && !source) return 1;
19
20 // To simplify calling code this fuction can be called with |source| == null
21 // and |source_sz| == 0. This and vp8dx_bool_decoder_fill() are essentially
22 // no-ops in this case.
23 // Work around a ubsan warning with a ternary to avoid adding 0 to null.
24 br->user_buffer_end = source ? source + source_sz : source;
25 br->user_buffer = source;
26 br->value = 0;
27 br->count = -8;
28 br->range = 255;
29 br->decrypt_cb = decrypt_cb;
30 br->decrypt_state = decrypt_state;
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 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 - CHAR_BIT - (count + CHAR_BIT);
43 size_t bytes_left = br->user_buffer_end - bufptr;
44 size_t bits_left = bytes_left * CHAR_BIT;
45 int x = shift + CHAR_BIT - (int)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 = VPXMIN(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 count += VP8_LOTS_OF_BITS;
57 loop_end = x;
58 }
59
60 if (x < 0 || bits_left) {
61 while (shift >= loop_end) {
62 count += CHAR_BIT;
63 value |= (VP8_BD_VALUE)*bufptr << shift;
64 ++bufptr;
65 ++br->user_buffer;
66 shift -= CHAR_BIT;
67 }
68 }
69
70 br->value = value;
71 br->count = count;
72 }
73