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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 #include <assert.h>
32 
33 #include "libavutil/intreadwrite.h"
34 #include "libavutil/avassert.h"
35 
36 typedef struct PutBitContext {
37  uint32_t bit_buf;
38  int bit_left;
42 
43 /**
44  * Initialize the PutBitContext s.
45  *
46  * @param buffer the buffer where to put bits
47  * @param buffer_size the size in bytes of buffer
48  */
49 static inline void init_put_bits(PutBitContext *s, uint8_t *buffer,
50  int buffer_size)
51 {
52  if (buffer_size < 0) {
53  buffer_size = 0;
54  buffer = NULL;
55  }
56 
57  s->size_in_bits = 8 * buffer_size;
58  s->buf = buffer;
59  s->buf_end = s->buf + buffer_size;
60  s->buf_ptr = s->buf;
61  s->bit_left = 32;
62  s->bit_buf = 0;
63 }
64 
65 /**
66  * Rebase the bit writer onto a reallocated buffer.
67  *
68  * @param buffer the buffer where to put bits
69  * @param buffer_size the size in bytes of buffer,
70  * must be larger than the previous size
71  */
73  int buffer_size)
74 {
75  av_assert0(8*buffer_size > s->size_in_bits);
76 
77  s->buf_end = buffer + buffer_size;
78  s->buf_ptr = buffer + (s->buf_ptr - s->buf);
79  s->buf = buffer;
80  s->size_in_bits = 8 * buffer_size;
81 }
82 
83 /**
84  * @return the total number of bits written to the bitstream.
85  */
86 static inline int put_bits_count(PutBitContext *s)
87 {
88  return (s->buf_ptr - s->buf) * 8 + 32 - s->bit_left;
89 }
90 
91 /**
92  * @return the number of bits available in the bitstream.
93  */
94 static inline int put_bits_left(PutBitContext* s)
95 {
96  return (s->buf_end - s->buf_ptr) * 8 - 32 + s->bit_left;
97 }
98 
99 /**
100  * Pad the end of the output stream with zeros.
101  */
102 static inline void flush_put_bits(PutBitContext *s)
103 {
104 #ifndef BITSTREAM_WRITER_LE
105  if (s->bit_left < 32)
106  s->bit_buf <<= s->bit_left;
107 #endif
108  while (s->bit_left < 32) {
109  /* XXX: should test end of buffer */
110 #ifdef BITSTREAM_WRITER_LE
111  *s->buf_ptr++ = s->bit_buf;
112  s->bit_buf >>= 8;
113 #else
114  *s->buf_ptr++ = s->bit_buf >> 24;
115  s->bit_buf <<= 8;
116 #endif
117  s->bit_left += 8;
118  }
119  s->bit_left = 32;
120  s->bit_buf = 0;
121 }
122 
123 #ifdef BITSTREAM_WRITER_LE
124 #define avpriv_align_put_bits align_put_bits_unsupported_here
125 #define avpriv_put_string ff_put_string_unsupported_here
126 #define avpriv_copy_bits avpriv_copy_bits_unsupported_here
127 #else
128 /**
129  * Pad the bitstream with zeros up to the next byte boundary.
130  */
132 
133 /**
134  * Put the string string in the bitstream.
135  *
136  * @param terminate_string 0-terminates the written string if value is 1
137  */
138 void avpriv_put_string(PutBitContext *pb, const char *string,
139  int terminate_string);
140 
141 /**
142  * Copy the content of src to the bitstream.
143  *
144  * @param length the number of bits of src to copy
145  */
146 void avpriv_copy_bits(PutBitContext *pb, const uint8_t *src, int length);
147 #endif
148 
149 /**
150  * Write up to 31 bits into a bitstream.
151  * Use put_bits32 to write 32 bits.
152  */
153 static inline void put_bits(PutBitContext *s, int n, unsigned int value)
154 {
155  unsigned int bit_buf;
156  int bit_left;
157 
158  av_assert2(n <= 31 && value < (1U << n));
159 
160  bit_buf = s->bit_buf;
161  bit_left = s->bit_left;
162 
163  /* XXX: optimize */
164 #ifdef BITSTREAM_WRITER_LE
165  bit_buf |= value << (32 - bit_left);
166  if (n >= bit_left) {
167  av_assert2(s->buf_ptr+3<s->buf_end);
168  AV_WL32(s->buf_ptr, bit_buf);
169  s->buf_ptr += 4;
170  bit_buf = (bit_left == 32) ? 0 : value >> bit_left;
171  bit_left += 32;
172  }
173  bit_left -= n;
174 #else
175  if (n < bit_left) {
176  bit_buf = (bit_buf << n) | value;
177  bit_left -= n;
178  } else {
179  bit_buf <<= bit_left;
180  bit_buf |= value >> (n - bit_left);
181  av_assert2(s->buf_ptr+3<s->buf_end);
182  AV_WB32(s->buf_ptr, bit_buf);
183  s->buf_ptr += 4;
184  bit_left += 32 - n;
185  bit_buf = value;
186  }
187 #endif
188 
189  s->bit_buf = bit_buf;
190  s->bit_left = bit_left;
191 }
192 
193 static inline void put_sbits(PutBitContext *pb, int n, int32_t value)
194 {
195  av_assert2(n >= 0 && n <= 31);
196 
197  put_bits(pb, n, value & ((1 << n) - 1));
198 }
199 
200 /**
201  * Write exactly 32 bits into a bitstream.
202  */
203 static void av_unused put_bits32(PutBitContext *s, uint32_t value)
204 {
205  int lo = value & 0xffff;
206  int hi = value >> 16;
207 #ifdef BITSTREAM_WRITER_LE
208  put_bits(s, 16, lo);
209  put_bits(s, 16, hi);
210 #else
211  put_bits(s, 16, hi);
212  put_bits(s, 16, lo);
213 #endif
214 }
215 
216 /**
217  * Return the pointer to the byte where the bitstream writer will put
218  * the next bit.
219  */
221 {
222  return s->buf_ptr;
223 }
224 
225 /**
226  * Skip the given number of bytes.
227  * PutBitContext must be flushed & aligned to a byte boundary before calling this.
228  */
229 static inline void skip_put_bytes(PutBitContext *s, int n)
230 {
231  av_assert2((put_bits_count(s) & 7) == 0);
232  av_assert2(s->bit_left == 32);
233  s->buf_ptr += n;
234 }
235 
236 /**
237  * Skip the given number of bits.
238  * Must only be used if the actual values in the bitstream do not matter.
239  * If n is 0 the behavior is undefined.
240  */
241 static inline void skip_put_bits(PutBitContext *s, int n)
242 {
243  s->bit_left -= n;
244  s->buf_ptr -= 4 * (s->bit_left >> 5);
245  s->bit_left &= 31;
246 }
247 
248 /**
249  * Change the end of the buffer.
250  *
251  * @param size the new size in bytes of the buffer where to put bits
252  */
253 static inline void set_put_bits_buffer_size(PutBitContext *s, int size)
254 {
255  s->buf_end = s->buf + size;
256 }
257 
258 #endif /* AVCODEC_PUT_BITS_H */