Rev 1624 | Details | Compare with Previous | Last modification | View Log | RSS feed
| Rev | Author | Line No. | Line |
|---|---|---|---|
| 1624 | giacomo | 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 |