ffmpeg/libavcodec/put_bits.h

   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;
  39     uint8_t *buf, *buf_ptr, *buf_end;
  40     int size_in_bits;
  41 } PutBitContext;
  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  */
  72 static inline void rebase_put_bits(PutBitContext *s, uint8_t *buffer,
  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  */
 131 void avpriv_align_put_bits(PutBitContext *s);
 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  */
 220 static inline uint8_t *put_bits_ptr(PutBitContext *s)
 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 */