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path: root/libavcodec/put_bits.h (plain)
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1/*
2 * copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
3 *
4 * This file is part of FFmpeg.
5 *
6 * FFmpeg is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU Lesser General Public
8 * License as published by the Free Software Foundation; either
9 * version 2.1 of the License, or (at your option) any later version.
10 *
11 * FFmpeg is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * Lesser General Public License for more details.
15 *
16 * You should have received a copy of the GNU Lesser General Public
17 * License along with FFmpeg; if not, write to the Free Software
18 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19 */
20
21/**
22 * @file
23 * bitstream writer API
24 */
25
26#ifndef AVCODEC_PUT_BITS_H
27#define AVCODEC_PUT_BITS_H
28
29#include <stdint.h>
30#include <stddef.h>
31
32#include "libavutil/intreadwrite.h"
33#include "libavutil/avassert.h"
34
35typedef struct PutBitContext {
36 uint32_t bit_buf;
37 int bit_left;
38 uint8_t *buf, *buf_ptr, *buf_end;
39 int size_in_bits;
40} PutBitContext;
41
42/**
43 * Initialize the PutBitContext s.
44 *
45 * @param buffer the buffer where to put bits
46 * @param buffer_size the size in bytes of buffer
47 */
48static inline void init_put_bits(PutBitContext *s, uint8_t *buffer,
49 int buffer_size)
50{
51 if (buffer_size < 0) {
52 buffer_size = 0;
53 buffer = NULL;
54 }
55
56 s->size_in_bits = 8 * buffer_size;
57 s->buf = buffer;
58 s->buf_end = s->buf + buffer_size;
59 s->buf_ptr = s->buf;
60 s->bit_left = 32;
61 s->bit_buf = 0;
62}
63
64/**
65 * Rebase the bit writer onto a reallocated buffer.
66 *
67 * @param buffer the buffer where to put bits
68 * @param buffer_size the size in bytes of buffer,
69 * must be larger than the previous size
70 */
71static inline void rebase_put_bits(PutBitContext *s, uint8_t *buffer,
72 int buffer_size)
73{
74 av_assert0(8*buffer_size > s->size_in_bits);
75
76 s->buf_end = buffer + buffer_size;
77 s->buf_ptr = buffer + (s->buf_ptr - s->buf);
78 s->buf = buffer;
79 s->size_in_bits = 8 * buffer_size;
80}
81
82/**
83 * @return the total number of bits written to the bitstream.
84 */
85static inline int put_bits_count(PutBitContext *s)
86{
87 return (s->buf_ptr - s->buf) * 8 + 32 - s->bit_left;
88}
89
90/**
91 * @return the number of bits available in the bitstream.
92 */
93static inline int put_bits_left(PutBitContext* s)
94{
95 return (s->buf_end - s->buf_ptr) * 8 - 32 + s->bit_left;
96}
97
98/**
99 * Pad the end of the output stream with zeros.
100 */
101static inline void flush_put_bits(PutBitContext *s)
102{
103#ifndef BITSTREAM_WRITER_LE
104 if (s->bit_left < 32)
105 s->bit_buf <<= s->bit_left;
106#endif
107 while (s->bit_left < 32) {
108 av_assert0(s->buf_ptr < s->buf_end);
109#ifdef BITSTREAM_WRITER_LE
110 *s->buf_ptr++ = s->bit_buf;
111 s->bit_buf >>= 8;
112#else
113 *s->buf_ptr++ = s->bit_buf >> 24;
114 s->bit_buf <<= 8;
115#endif
116 s->bit_left += 8;
117 }
118 s->bit_left = 32;
119 s->bit_buf = 0;
120}
121
122#ifdef BITSTREAM_WRITER_LE
123#define avpriv_align_put_bits align_put_bits_unsupported_here
124#define avpriv_put_string ff_put_string_unsupported_here
125#define avpriv_copy_bits avpriv_copy_bits_unsupported_here
126#else
127/**
128 * Pad the bitstream with zeros up to the next byte boundary.
129 */
130void avpriv_align_put_bits(PutBitContext *s);
131
132/**
133 * Put the string string in the bitstream.
134 *
135 * @param terminate_string 0-terminates the written string if value is 1
136 */
137void avpriv_put_string(PutBitContext *pb, const char *string,
138 int terminate_string);
139
140/**
141 * Copy the content of src to the bitstream.
142 *
143 * @param length the number of bits of src to copy
144 */
145void avpriv_copy_bits(PutBitContext *pb, const uint8_t *src, int length);
146#endif
147
148/**
149 * Write up to 31 bits into a bitstream.
150 * Use put_bits32 to write 32 bits.
151 */
152static inline void put_bits(PutBitContext *s, int n, unsigned int value)
153{
154 unsigned int bit_buf;
155 int bit_left;
156
157 av_assert2(n <= 31 && value < (1U << n));
158
159 bit_buf = s->bit_buf;
160 bit_left = s->bit_left;
161
162 /* XXX: optimize */
163#ifdef BITSTREAM_WRITER_LE
164 bit_buf |= value << (32 - bit_left);
165 if (n >= bit_left) {
166 if (3 < s->buf_end - s->buf_ptr) {
167 AV_WL32(s->buf_ptr, bit_buf);
168 s->buf_ptr += 4;
169 } else {
170 av_log(NULL, AV_LOG_ERROR, "Internal error, put_bits buffer too small\n");
171 av_assert2(0);
172 }
173 bit_buf = value >> bit_left;
174 bit_left += 32;
175 }
176 bit_left -= n;
177#else
178 if (n < bit_left) {
179 bit_buf = (bit_buf << n) | value;
180 bit_left -= n;
181 } else {
182 bit_buf <<= bit_left;
183 bit_buf |= value >> (n - bit_left);
184 if (3 < s->buf_end - s->buf_ptr) {
185 AV_WB32(s->buf_ptr, bit_buf);
186 s->buf_ptr += 4;
187 } else {
188 av_log(NULL, AV_LOG_ERROR, "Internal error, put_bits buffer too small\n");
189 av_assert2(0);
190 }
191 bit_left += 32 - n;
192 bit_buf = value;
193 }
194#endif
195
196 s->bit_buf = bit_buf;
197 s->bit_left = bit_left;
198}
199
200static inline void put_sbits(PutBitContext *pb, int n, int32_t value)
201{
202 av_assert2(n >= 0 && n <= 31);
203
204 put_bits(pb, n, av_mod_uintp2(value, n));
205}
206
207/**
208 * Write exactly 32 bits into a bitstream.
209 */
210static void av_unused put_bits32(PutBitContext *s, uint32_t value)
211{
212 int lo = value & 0xffff;
213 int hi = value >> 16;
214#ifdef BITSTREAM_WRITER_LE
215 put_bits(s, 16, lo);
216 put_bits(s, 16, hi);
217#else
218 put_bits(s, 16, hi);
219 put_bits(s, 16, lo);
220#endif
221}
222
223/**
224 * Return the pointer to the byte where the bitstream writer will put
225 * the next bit.
226 */
227static inline uint8_t *put_bits_ptr(PutBitContext *s)
228{
229 return s->buf_ptr;
230}
231
232/**
233 * Skip the given number of bytes.
234 * PutBitContext must be flushed & aligned to a byte boundary before calling this.
235 */
236static inline void skip_put_bytes(PutBitContext *s, int n)
237{
238 av_assert2((put_bits_count(s) & 7) == 0);
239 av_assert2(s->bit_left == 32);
240 av_assert0(n <= s->buf_end - s->buf_ptr);
241 s->buf_ptr += n;
242}
243
244/**
245 * Skip the given number of bits.
246 * Must only be used if the actual values in the bitstream do not matter.
247 * If n is 0 the behavior is undefined.
248 */
249static inline void skip_put_bits(PutBitContext *s, int n)
250{
251 s->bit_left -= n;
252 s->buf_ptr -= 4 * (s->bit_left >> 5);
253 s->bit_left &= 31;
254}
255
256/**
257 * Change the end of the buffer.
258 *
259 * @param size the new size in bytes of the buffer where to put bits
260 */
261static inline void set_put_bits_buffer_size(PutBitContext *s, int size)
262{
263 av_assert0(size <= INT_MAX/8 - 32);
264 s->buf_end = s->buf + size;
265 s->size_in_bits = 8*size;
266}
267
268#endif /* AVCODEC_PUT_BITS_H */
269
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