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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 <stdlib.h>
31 #include <assert.h>
32 
33 #include "libavutil/bswap.h"
34 #include "libavutil/common.h"
35 #include "libavutil/intreadwrite.h"
36 #include "libavutil/log.h"
37 #include "libavutil/avassert.h"
38 #include "mathops.h"
39 #include "config.h"
40 
41 typedef struct PutBitContext {
42  uint32_t bit_buf;
43  int bit_left;
47 
48 /**
49  * Initialize the PutBitContext s.
50  *
51  * @param buffer the buffer where to put bits
52  * @param buffer_size the size in bytes of buffer
53  */
54 static inline void init_put_bits(PutBitContext *s, uint8_t *buffer,
55  int buffer_size)
56 {
57  if (buffer_size < 0) {
58  buffer_size = 0;
59  buffer = NULL;
60  }
61 
62  s->size_in_bits = 8 * buffer_size;
63  s->buf = buffer;
64  s->buf_end = s->buf + buffer_size;
65  s->buf_ptr = s->buf;
66  s->bit_left = 32;
67  s->bit_buf = 0;
68 }
69 
70 /**
71  * @return the total number of bits written to the bitstream.
72  */
73 static inline int put_bits_count(PutBitContext *s)
74 {
75  return (s->buf_ptr - s->buf) * 8 + 32 - s->bit_left;
76 }
77 
78 /**
79  * Pad the end of the output stream with zeros.
80  */
81 static inline void flush_put_bits(PutBitContext *s)
82 {
83 #ifndef BITSTREAM_WRITER_LE
84  if (s->bit_left < 32)
85  s->bit_buf <<= s->bit_left;
86 #endif
87  while (s->bit_left < 32) {
88  /* XXX: should test end of buffer */
89 #ifdef BITSTREAM_WRITER_LE
90  *s->buf_ptr++ = s->bit_buf;
91  s->bit_buf >>= 8;
92 #else
93  *s->buf_ptr++ = s->bit_buf >> 24;
94  s->bit_buf <<= 8;
95 #endif
96  s->bit_left += 8;
97  }
98  s->bit_left = 32;
99  s->bit_buf = 0;
100 }
101 
102 #ifdef BITSTREAM_WRITER_LE
103 #define avpriv_align_put_bits align_put_bits_unsupported_here
104 #define avpriv_put_string ff_put_string_unsupported_here
105 #define avpriv_copy_bits avpriv_copy_bits_unsupported_here
106 #else
107 /**
108  * Pad the bitstream with zeros up to the next byte boundary.
109  */
111 
112 /**
113  * Put the string string in the bitstream.
114  *
115  * @param terminate_string 0-terminates the written string if value is 1
116  */
117 void avpriv_put_string(PutBitContext *pb, const char *string,
118  int terminate_string);
119 
120 /**
121  * Copy the content of src to the bitstream.
122  *
123  * @param length the number of bits of src to copy
124  */
125 void avpriv_copy_bits(PutBitContext *pb, const uint8_t *src, int length);
126 #endif
127 
128 /**
129  * Write up to 31 bits into a bitstream.
130  * Use put_bits32 to write 32 bits.
131  */
132 static inline void put_bits(PutBitContext *s, int n, unsigned int value)
133 {
134  unsigned int bit_buf;
135  int bit_left;
136 
137  av_assert2(n <= 31 && value < (1U << n));
138 
139  bit_buf = s->bit_buf;
140  bit_left = s->bit_left;
141 
142  /* XXX: optimize */
143 #ifdef BITSTREAM_WRITER_LE
144  bit_buf |= value << (32 - bit_left);
145  if (n >= bit_left) {
146  av_assert2(s->buf_ptr+3<s->buf_end);
147  AV_WL32(s->buf_ptr, bit_buf);
148  s->buf_ptr += 4;
149  bit_buf = (bit_left == 32) ? 0 : value >> bit_left;
150  bit_left += 32;
151  }
152  bit_left -= n;
153 #else
154  if (n < bit_left) {
155  bit_buf = (bit_buf << n) | value;
156  bit_left -= n;
157  } else {
158  bit_buf <<= bit_left;
159  bit_buf |= value >> (n - bit_left);
160  av_assert2(s->buf_ptr+3<s->buf_end);
161  AV_WB32(s->buf_ptr, bit_buf);
162  s->buf_ptr += 4;
163  bit_left += 32 - n;
164  bit_buf = value;
165  }
166 #endif
167 
168  s->bit_buf = bit_buf;
169  s->bit_left = bit_left;
170 }
171 
172 static inline void put_sbits(PutBitContext *pb, int n, int32_t value)
173 {
174  av_assert2(n >= 0 && n <= 31);
175 
176  put_bits(pb, n, value & ((1 << n) - 1));
177 }
178 
179 /**
180  * Write exactly 32 bits into a bitstream.
181  */
182 static void av_unused put_bits32(PutBitContext *s, uint32_t value)
183 {
184  int lo = value & 0xffff;
185  int hi = value >> 16;
186 #ifdef BITSTREAM_WRITER_LE
187  put_bits(s, 16, lo);
188  put_bits(s, 16, hi);
189 #else
190  put_bits(s, 16, hi);
191  put_bits(s, 16, lo);
192 #endif
193 }
194 
195 /**
196  * Return the pointer to the byte where the bitstream writer will put
197  * the next bit.
198  */
200 {
201  return s->buf_ptr;
202 }
203 
204 /**
205  * Skip the given number of bytes.
206  * PutBitContext must be flushed & aligned to a byte boundary before calling this.
207  */
208 static inline void skip_put_bytes(PutBitContext *s, int n)
209 {
210  av_assert2((put_bits_count(s) & 7) == 0);
211  av_assert2(s->bit_left == 32);
212  s->buf_ptr += n;
213 }
214 
215 /**
216  * Skip the given number of bits.
217  * Must only be used if the actual values in the bitstream do not matter.
218  * If n is 0 the behavior is undefined.
219  */
220 static inline void skip_put_bits(PutBitContext *s, int n)
221 {
222  s->bit_left -= n;
223  s->buf_ptr -= 4 * (s->bit_left >> 5);
224  s->bit_left &= 31;
225 }
226 
227 /**
228  * Change the end of the buffer.
229  *
230  * @param size the new size in bytes of the buffer where to put bits
231  */
232 static inline void set_put_bits_buffer_size(PutBitContext *s, int size)
233 {
234  s->buf_end = s->buf + size;
235 }
236 
237 #endif /* AVCODEC_PUT_BITS_H */