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