1 /* getbits.c, bit level routines */
4 * All modifications (mpeg2decode -> mpeg2play) are
5 * Copyright (C) 1996, Stefan Eckart. All Rights Reserved.
8 /* Copyright (C) 1996, MPEG Software Simulation Group. All Rights Reserved. */
11 * Disclaimer of Warranty
13 * These software programs are available to the user without any license fee or
14 * royalty on an "as is" basis. The MPEG Software Simulation Group disclaims
15 * any and all warranties, whether express, implied, or statuary, including any
16 * implied warranties or merchantability or of fitness for a particular
17 * purpose. In no event shall the copyright-holder be liable for any
18 * incidental, punitive, or consequential damages of any kind whatsoever
19 * arising from the use of these programs.
21 * This disclaimer of warranty extends to the user of these programs and user's
22 * customers, employees, agents, transferees, successors, and assigns.
24 * The MPEG Software Simulation Group does not represent or warrant that the
25 * programs furnished hereunder are free of infringement of any third-party
28 * Commercial implementations of MPEG-1 and MPEG-2 video, including shareware,
29 * are subject to royalty fees to patent holders. Many of these patents are
30 * general enough such that they are unavoidable regardless of implementation
38 /* initialize buffer, call once before first getbits or showbits */
40 void Initialize_Buffer()
43 ld->Rdptr = ld->Rdbfr + 2048;
44 ld->Rdmax = ld->Rdptr;
47 /* only the verifier uses this particular bit counter
48 * Bitcnt keeps track of the current parser position with respect
49 * to the video elementary stream being decoded, regardless
50 * of whether or not it is wrapped within a systems layer stream
56 Flush_Buffer(0); /* fills valid data into bfr */
63 /*Buffer_Level = read(ld->Infile,ld->Rdbfr,2048);*/
64 Buffer_Level = ld->read_stream(ld->Infile,ld->Rdbfr,2048);
65 ld->Rdptr = ld->Rdbfr;
67 if (System_Stream_Flag)
71 /* end of the bitstream file */
72 if (Buffer_Level < 2048)
78 /* pad until the next to the next 32-bit word boundary */
79 while (Buffer_Level & 3)
80 ld->Rdbfr[Buffer_Level++] = 0;
82 /* pad the buffer with sequence end codes */
83 while (Buffer_Level < 2048)
85 ld->Rdbfr[Buffer_Level++] = SEQUENCE_END_CODE>>24;
86 ld->Rdbfr[Buffer_Level++] = SEQUENCE_END_CODE>>16;
87 ld->Rdbfr[Buffer_Level++] = SEQUENCE_END_CODE>>8;
88 ld->Rdbfr[Buffer_Level++] = SEQUENCE_END_CODE&0xff;
94 /* MPEG-1 system layer demultiplexer */
98 while(ld->Rdptr >= ld->Rdbfr+2048)
100 /*read(ld->Infile,ld->Rdbfr,2048);*/
101 ld->read_stream(ld->Infile,ld->Rdbfr,2048);
108 /* extract a 16-bit word from the bitstream buffer */
114 return (Val<<8) | Get_Byte();
118 /* return next n bits (right adjusted) without advancing */
120 unsigned int Show_Bits(N)
123 return ld->Bfr >> (32-N);
127 /* return next bit (could be made faster than Get_Bits(1)) */
129 unsigned int Get_Bits1()
135 /* advance by n bits */
144 Incnt = ld->Incnt -= N;
148 if (System_Stream_Flag && (ld->Rdptr >= ld->Rdmax-4))
152 if (ld->Rdptr >= ld->Rdmax)
154 ld->Bfr |= Get_Byte() << (24 - Incnt);
159 else if (ld->Rdptr < ld->Rdbfr+2044)
163 ld->Bfr |= *ld->Rdptr++ << (24 - Incnt);
172 if (ld->Rdptr >= ld->Rdbfr+2048)
174 ld->Bfr |= *ld->Rdptr++ << (24 - Incnt);
189 /* return next n bits (right adjusted) */
191 unsigned int Get_Bits(N)