/src/libde265/libde265/bitstream.cc
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1 | | /* |
2 | | * H.265 video codec. |
3 | | * Copyright (c) 2013-2014 struktur AG, Dirk Farin <farin@struktur.de> |
4 | | * |
5 | | * This file is part of libde265. |
6 | | * |
7 | | * libde265 is free software: you can redistribute it and/or modify |
8 | | * it under the terms of the GNU Lesser General Public License as |
9 | | * published by the Free Software Foundation, either version 3 of |
10 | | * the License, or (at your option) any later version. |
11 | | * |
12 | | * libde265 is distributed in the hope that it will be useful, |
13 | | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
14 | | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
15 | | * GNU Lesser General Public License for more details. |
16 | | * |
17 | | * You should have received a copy of the GNU Lesser General Public License |
18 | | * along with libde265. If not, see <http://www.gnu.org/licenses/>. |
19 | | */ |
20 | | |
21 | | #include "bitstream.h" |
22 | | #include "de265.h" |
23 | | |
24 | | #include <stdlib.h> |
25 | | #include <string.h> |
26 | | #include <assert.h> |
27 | | |
28 | | |
29 | | |
30 | | void bitreader_init(bitreader* br, unsigned char* buffer, int len) |
31 | 0 | { |
32 | 0 | br->data = buffer; |
33 | 0 | br->bytes_remaining = len; |
34 | |
|
35 | 0 | br->nextbits=0; |
36 | 0 | br->nextbits_cnt=0; |
37 | |
|
38 | 0 | bitreader_refill(br); |
39 | 0 | } |
40 | | |
41 | | void bitreader_refill(bitreader* br) |
42 | 0 | { |
43 | 0 | int shift = 64-br->nextbits_cnt; |
44 | |
|
45 | 0 | while (shift >= 8 && br->bytes_remaining) { |
46 | 0 | uint64_t newval = *br->data++; |
47 | 0 | br->bytes_remaining--; |
48 | |
|
49 | 0 | shift -= 8; |
50 | 0 | newval <<= shift; |
51 | 0 | br->nextbits |= newval; |
52 | 0 | } |
53 | |
|
54 | 0 | br->nextbits_cnt = 64-shift; |
55 | 0 | } |
56 | | |
57 | | int get_bits(bitreader* br, int n) |
58 | 0 | { |
59 | 0 | if (br->nextbits_cnt < n) { |
60 | 0 | bitreader_refill(br); |
61 | 0 | } |
62 | |
|
63 | 0 | uint64_t val = br->nextbits; |
64 | 0 | val >>= 64-n; |
65 | |
|
66 | 0 | br->nextbits <<= n; |
67 | 0 | br->nextbits_cnt -= n; |
68 | |
|
69 | 0 | return val; |
70 | 0 | } |
71 | | |
72 | | int get_bits_fast(bitreader* br, int n) |
73 | 0 | { |
74 | 0 | assert(br->nextbits_cnt >= n); |
75 | | |
76 | 0 | uint64_t val = br->nextbits; |
77 | 0 | val >>= 64-n; |
78 | |
|
79 | 0 | br->nextbits <<= n; |
80 | 0 | br->nextbits_cnt -= n; |
81 | |
|
82 | 0 | return val; |
83 | 0 | } |
84 | | |
85 | | int peek_bits(bitreader* br, int n) |
86 | 0 | { |
87 | 0 | if (br->nextbits_cnt < n) { |
88 | 0 | bitreader_refill(br); |
89 | 0 | } |
90 | |
|
91 | 0 | uint64_t val = br->nextbits; |
92 | 0 | val >>= 64-n; |
93 | |
|
94 | 0 | return val; |
95 | 0 | } |
96 | | |
97 | | void skip_bits(bitreader* br, int n) |
98 | 0 | { |
99 | 0 | if (br->nextbits_cnt < n) { |
100 | 0 | bitreader_refill(br); |
101 | 0 | } |
102 | |
|
103 | 0 | br->nextbits <<= n; |
104 | 0 | br->nextbits_cnt -= n; |
105 | 0 | } |
106 | | |
107 | | void skip_bits_fast(bitreader* br, int n) |
108 | 0 | { |
109 | 0 | br->nextbits <<= n; |
110 | 0 | br->nextbits_cnt -= n; |
111 | 0 | } |
112 | | |
113 | | void skip_to_byte_boundary(bitreader* br) |
114 | 0 | { |
115 | 0 | int nskip = (br->nextbits_cnt & 7); |
116 | |
|
117 | 0 | br->nextbits <<= nskip; |
118 | 0 | br->nextbits_cnt -= nskip; |
119 | 0 | } |
120 | | |
121 | | void prepare_for_CABAC(bitreader* br) |
122 | 0 | { |
123 | 0 | skip_to_byte_boundary(br); |
124 | |
|
125 | 0 | int rewind = br->nextbits_cnt/8; |
126 | 0 | br->data -= rewind; |
127 | 0 | br->bytes_remaining += rewind; |
128 | 0 | br->nextbits = 0; |
129 | 0 | br->nextbits_cnt = 0; |
130 | 0 | } |
131 | | |
132 | | int get_uvlc(bitreader* br) |
133 | 0 | { |
134 | 0 | int num_zeros=0; |
135 | |
|
136 | 0 | while (get_bits(br,1)==0) { |
137 | 0 | num_zeros++; |
138 | |
|
139 | 0 | if (num_zeros > MAX_UVLC_LEADING_ZEROS) { return UVLC_ERROR; } |
140 | 0 | } |
141 | | |
142 | 0 | int offset = 0; |
143 | 0 | if (num_zeros != 0) { |
144 | 0 | offset = get_bits(br, num_zeros); |
145 | 0 | int value = offset + (1<<num_zeros)-1; |
146 | 0 | assert(value>0); |
147 | 0 | return value; |
148 | 0 | } else { |
149 | 0 | return 0; |
150 | 0 | } |
151 | 0 | } |
152 | | |
153 | | int get_svlc(bitreader* br) |
154 | 0 | { |
155 | 0 | int v = get_uvlc(br); |
156 | 0 | if (v==0) return v; |
157 | 0 | if (v==UVLC_ERROR) return UVLC_ERROR; |
158 | | |
159 | 0 | bool negative = ((v&1)==0); |
160 | 0 | return negative ? -v/2 : (v+1)/2; |
161 | 0 | } |
162 | | |
163 | | bool check_rbsp_trailing_bits(bitreader* br) |
164 | 0 | { |
165 | 0 | int stop_bit = get_bits(br,1); |
166 | 0 | assert(stop_bit==1); |
167 | | |
168 | 0 | while (br->nextbits_cnt>0 || br->bytes_remaining>0) { |
169 | 0 | int filler = get_bits(br,1); |
170 | 0 | if (filler!=0) { |
171 | 0 | return false; |
172 | 0 | } |
173 | 0 | } |
174 | | |
175 | 0 | return true; |
176 | 0 | } |