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
15int 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
38void 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