xref: /aosp_15_r20/external/libvpx/vp8/decoder/dboolhuff.c (revision fb1b10ab9aebc7c7068eedab379b749d7e3900be)
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