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put_bits.h
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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 
35 typedef struct PutBitContext {
36  uint32_t bit_buf;
37  int bit_left;
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  */
48 static 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  */
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  */
85 static 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  */
93 static 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  */
101 static 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  /* XXX: should test end of buffer */
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  */
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  */
137 void 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  */
145 void 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  */
152 static 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  av_assert2(s->buf_ptr+3<s->buf_end);
167  AV_WL32(s->buf_ptr, bit_buf);
168  s->buf_ptr += 4;
169  bit_buf = (bit_left == 32) ? 0 : value >> bit_left;
170  bit_left += 32;
171  }
172  bit_left -= n;
173 #else
174  if (n < bit_left) {
175  bit_buf = (bit_buf << n) | value;
176  bit_left -= n;
177  } else {
178  bit_buf <<= bit_left;
179  bit_buf |= value >> (n - bit_left);
180  av_assert2(s->buf_ptr+3<s->buf_end);
181  AV_WB32(s->buf_ptr, bit_buf);
182  s->buf_ptr += 4;
183  bit_left += 32 - n;
184  bit_buf = value;
185  }
186 #endif
187 
188  s->bit_buf = bit_buf;
189  s->bit_left = bit_left;
190 }
191 
192 static inline void put_sbits(PutBitContext *pb, int n, int32_t value)
193 {
194  av_assert2(n >= 0 && n <= 31);
195 
196  put_bits(pb, n, value & ((1 << n) - 1));
197 }
198 
199 /**
200  * Write exactly 32 bits into a bitstream.
201  */
202 static void av_unused put_bits32(PutBitContext *s, uint32_t value)
203 {
204  int lo = value & 0xffff;
205  int hi = value >> 16;
206 #ifdef BITSTREAM_WRITER_LE
207  put_bits(s, 16, lo);
208  put_bits(s, 16, hi);
209 #else
210  put_bits(s, 16, hi);
211  put_bits(s, 16, lo);
212 #endif
213 }
214 
215 /**
216  * Return the pointer to the byte where the bitstream writer will put
217  * the next bit.
218  */
220 {
221  return s->buf_ptr;
222 }
223 
224 /**
225  * Skip the given number of bytes.
226  * PutBitContext must be flushed & aligned to a byte boundary before calling this.
227  */
228 static inline void skip_put_bytes(PutBitContext *s, int n)
229 {
230  av_assert2((put_bits_count(s) & 7) == 0);
231  av_assert2(s->bit_left == 32);
232  s->buf_ptr += n;
233 }
234 
235 /**
236  * Skip the given number of bits.
237  * Must only be used if the actual values in the bitstream do not matter.
238  * If n is 0 the behavior is undefined.
239  */
240 static inline void skip_put_bits(PutBitContext *s, int n)
241 {
242  s->bit_left -= n;
243  s->buf_ptr -= 4 * (s->bit_left >> 5);
244  s->bit_left &= 31;
245 }
246 
247 /**
248  * Change the end of the buffer.
249  *
250  * @param size the new size in bytes of the buffer where to put bits
251  */
252 static inline void set_put_bits_buffer_size(PutBitContext *s, int size)
253 {
254  s->buf_end = s->buf + size;
255 }
256 
257 #endif /* AVCODEC_PUT_BITS_H */