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Rev | Author | Line No. | Line |
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1085 | pj | 1 | /* getbits.c, bit level routines */ |
2 | |||
3 | /* |
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4 | * All modifications (mpeg2decode -> mpeg2play) are |
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5 | * Copyright (C) 1996, Stefan Eckart. All Rights Reserved. |
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6 | */ |
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7 | |||
8 | /* Copyright (C) 1996, MPEG Software Simulation Group. All Rights Reserved. */ |
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9 | |||
10 | /* |
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11 | * Disclaimer of Warranty |
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12 | * |
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13 | * These software programs are available to the user without any license fee or |
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14 | * royalty on an "as is" basis. The MPEG Software Simulation Group disclaims |
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15 | * any and all warranties, whether express, implied, or statuary, including any |
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16 | * implied warranties or merchantability or of fitness for a particular |
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17 | * purpose. In no event shall the copyright-holder be liable for any |
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18 | * incidental, punitive, or consequential damages of any kind whatsoever |
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19 | * arising from the use of these programs. |
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20 | * |
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21 | * This disclaimer of warranty extends to the user of these programs and user's |
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22 | * customers, employees, agents, transferees, successors, and assigns. |
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23 | * |
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24 | * The MPEG Software Simulation Group does not represent or warrant that the |
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25 | * programs furnished hereunder are free of infringement of any third-party |
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26 | * patents. |
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27 | * |
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28 | * Commercial implementations of MPEG-1 and MPEG-2 video, including shareware, |
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29 | * are subject to royalty fees to patent holders. Many of these patents are |
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30 | * general enough such that they are unavoidable regardless of implementation |
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31 | * design. |
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32 | * |
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33 | */ |
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34 | |||
35 | #include <stdio.h> |
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36 | #include <stdlib.h> |
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37 | |||
38 | #include "config.h" |
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39 | #include "global.h" |
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40 | |||
41 | /* initialize buffer, call once before first getbits or showbits */ |
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42 | |||
43 | void Initialize_Buffer() |
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44 | { |
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45 | ld->Incnt = 0; |
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46 | ld->Rdptr = ld->Rdbfr + 2048; |
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47 | ld->Rdmax = ld->Rdptr; |
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48 | |||
49 | #ifdef VERIFY |
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50 | /* only the verifier uses this particular bit counter |
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51 | * Bitcnt keeps track of the current parser position with respect |
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52 | * to the video elementary stream being decoded, regardless |
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53 | * of whether or not it is wrapped within a systems layer stream |
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54 | */ |
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55 | ld->Bitcnt = 0; |
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56 | #endif |
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57 | |||
58 | ld->Bfr = 0; |
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59 | Flush_Buffer(0); /* fills valid data into bfr */ |
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60 | } |
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61 | |||
62 | void Fill_Buffer() |
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63 | { |
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64 | int Buffer_Level; |
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65 | |||
66 | Buffer_Level = read(ld->Infile,ld->Rdbfr,2048); |
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67 | ld->Rdptr = ld->Rdbfr; |
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68 | |||
69 | if (System_Stream_Flag) |
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70 | ld->Rdmax -= 2048; |
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71 | |||
72 | |||
73 | /* end of the bitstream file */ |
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74 | if (Buffer_Level < 2048) |
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75 | { |
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76 | /* just to be safe */ |
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77 | if (Buffer_Level < 0) |
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78 | Buffer_Level = 0; |
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79 | |||
80 | /* pad until the next to the next 32-bit word boundary */ |
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81 | while (Buffer_Level & 3) |
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82 | ld->Rdbfr[Buffer_Level++] = 0; |
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83 | |||
84 | /* pad the buffer with sequence end codes */ |
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85 | while (Buffer_Level < 2048) |
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86 | { |
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87 | ld->Rdbfr[Buffer_Level++] = SEQUENCE_END_CODE>>24; |
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88 | ld->Rdbfr[Buffer_Level++] = SEQUENCE_END_CODE>>16; |
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89 | ld->Rdbfr[Buffer_Level++] = SEQUENCE_END_CODE>>8; |
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90 | ld->Rdbfr[Buffer_Level++] = SEQUENCE_END_CODE&0xff; |
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91 | } |
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92 | } |
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93 | } |
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94 | |||
95 | |||
96 | /* MPEG-1 system layer demultiplexer */ |
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97 | |||
98 | int Get_Byte() |
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99 | { |
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100 | while(ld->Rdptr >= ld->Rdbfr+2048) |
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101 | { |
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102 | read(ld->Infile,ld->Rdbfr,2048); |
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103 | ld->Rdptr -= 2048; |
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104 | ld->Rdmax -= 2048; |
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105 | } |
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106 | return *ld->Rdptr++; |
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107 | } |
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108 | |||
109 | /* extract a 16-bit word from the bitstream buffer */ |
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110 | int Get_Word() |
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111 | { |
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112 | int Val; |
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113 | |||
114 | Val = Get_Byte(); |
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115 | return (Val<<8) | Get_Byte(); |
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116 | } |
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117 | |||
118 | |||
119 | /* return next n bits (right adjusted) without advancing */ |
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120 | |||
121 | unsigned int Show_Bits(N) |
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122 | int N; |
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123 | { |
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124 | return ld->Bfr >> (32-N); |
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125 | } |
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126 | |||
127 | |||
128 | /* return next bit (could be made faster than Get_Bits(1)) */ |
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129 | |||
130 | unsigned int Get_Bits1() |
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131 | { |
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132 | return Get_Bits(1); |
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133 | } |
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134 | |||
135 | |||
136 | /* advance by n bits */ |
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137 | |||
138 | void Flush_Buffer(N) |
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139 | int N; |
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140 | { |
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141 | int Incnt; |
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142 | |||
143 | ld->Bfr <<= N; |
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144 | |||
145 | Incnt = ld->Incnt -= N; |
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146 | |||
147 | if (Incnt <= 24) |
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148 | { |
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149 | if (System_Stream_Flag && (ld->Rdptr >= ld->Rdmax-4)) |
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150 | { |
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151 | do |
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152 | { |
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153 | if (ld->Rdptr >= ld->Rdmax) |
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154 | Next_Packet(); |
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155 | ld->Bfr |= Get_Byte() << (24 - Incnt); |
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156 | Incnt += 8; |
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157 | } |
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158 | while (Incnt <= 24); |
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159 | } |
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160 | else if (ld->Rdptr < ld->Rdbfr+2044) |
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161 | { |
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162 | do |
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163 | { |
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164 | ld->Bfr |= *ld->Rdptr++ << (24 - Incnt); |
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165 | Incnt += 8; |
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166 | } |
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167 | while (Incnt <= 24); |
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168 | } |
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169 | else |
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170 | { |
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171 | do |
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172 | { |
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173 | if (ld->Rdptr >= ld->Rdbfr+2048) |
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174 | Fill_Buffer(); |
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175 | ld->Bfr |= *ld->Rdptr++ << (24 - Incnt); |
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176 | Incnt += 8; |
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177 | } |
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178 | while (Incnt <= 24); |
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179 | } |
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180 | ld->Incnt = Incnt; |
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181 | } |
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182 | |||
183 | #ifdef VERIFY |
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184 | ld->Bitcnt += N; |
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185 | #endif /* VERIFY */ |
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186 | |||
187 | } |
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188 | |||
189 | |||
190 | /* return next n bits (right adjusted) */ |
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191 | |||
192 | unsigned int Get_Bits(N) |
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193 | int N; |
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194 | { |
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195 | unsigned int Val; |
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196 | |||
197 | Val = Show_Bits(N); |
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198 | Flush_Buffer(N); |
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199 | |||
200 | return Val; |
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201 | } |
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202 |