getbits.c
资源名称:mpeg2编解码.zip [点击查看]
上传用户:hkgotone
上传日期:2013-02-17
资源大小:293k
文件大小:4k
源码类别:
Windows Mobile
开发平台:
C/C++
- /* getbits.c, bit level routines */
- /*
- * All modifications (mpeg2decode -> mpeg2play) are
- * Copyright (C) 1996, Stefan Eckart. All Rights Reserved.
- */
- /* Copyright (C) 1996, MPEG Software Simulation Group. All Rights Reserved. */
- /*
- * Disclaimer of Warranty
- *
- * These software programs are available to the user without any license fee or
- * royalty on an "as is" basis. The MPEG Software Simulation Group disclaims
- * any and all warranties, whether express, implied, or statuary, including any
- * implied warranties or merchantability or of fitness for a particular
- * purpose. In no event shall the copyright-holder be liable for any
- * incidental, punitive, or consequential damages of any kind whatsoever
- * arising from the use of these programs.
- *
- * This disclaimer of warranty extends to the user of these programs and user's
- * customers, employees, agents, transferees, successors, and assigns.
- *
- * The MPEG Software Simulation Group does not represent or warrant that the
- * programs furnished hereunder are free of infringement of any third-party
- * patents.
- *
- * Commercial implementations of MPEG-1 and MPEG-2 video, including shareware,
- * are subject to royalty fees to patent holders. Many of these patents are
- * general enough such that they are unavoidable regardless of implementation
- * design.
- *
- */
- #include <stdio.h>
- #include <stdlib.h>
- #include "config.h"
- #include "global.h"
- /* initialize buffer, call once before first getbits or showbits */
- void Initialize_Buffer()
- {
- ld->Incnt = 0;
- ld->Rdptr = ld->Rdbfr + 2048;
- ld->Rdmax = ld->Rdptr;
- #ifdef VERIFY
- /* only the verifier uses this particular bit counter
- * Bitcnt keeps track of the current parser position with respect
- * to the video elementary stream being decoded, regardless
- * of whether or not it is wrapped within a systems layer stream
- */
- ld->Bitcnt = 0;
- #endif
- ld->Bfr = 0;
- Flush_Buffer(0); /* fills valid data into bfr */
- }
- void Fill_Buffer()
- {
- int Buffer_Level;
- Buffer_Level = read(ld->Infile,ld->Rdbfr,2048);
- ld->Rdptr = ld->Rdbfr;
- if (System_Stream_Flag)
- ld->Rdmax -= 2048;
- /* end of the bitstream file */
- if (Buffer_Level < 2048)
- {
- /* just to be safe */
- if (Buffer_Level < 0)
- Buffer_Level = 0;
- /* pad until the next to the next 32-bit word boundary */
- while (Buffer_Level & 3)
- ld->Rdbfr[Buffer_Level++] = 0;
- /* pad the buffer with sequence end codes */
- while (Buffer_Level < 2048)
- {
- ld->Rdbfr[Buffer_Level++] = SEQUENCE_END_CODE>>24;
- ld->Rdbfr[Buffer_Level++] = SEQUENCE_END_CODE>>16;
- ld->Rdbfr[Buffer_Level++] = SEQUENCE_END_CODE>>8;
- ld->Rdbfr[Buffer_Level++] = SEQUENCE_END_CODE&0xff;
- }
- }
- }
- /* MPEG-1 system layer demultiplexer */
- int Get_Byte()
- {
- while(ld->Rdptr >= ld->Rdbfr+2048)
- {
- read(ld->Infile,ld->Rdbfr,2048);
- ld->Rdptr -= 2048;
- ld->Rdmax -= 2048;
- }
- return *ld->Rdptr++;
- }
- /* extract a 16-bit word from the bitstream buffer */
- int Get_Word()
- {
- int Val;
- Val = Get_Byte();
- return (Val<<8) | Get_Byte();
- }
- /* return next n bits (right adjusted) without advancing */
- unsigned int Show_Bits(N)
- int N;
- {
- return ld->Bfr >> (32-N);
- }
- /* return next bit (could be made faster than Get_Bits(1)) */
- unsigned int Get_Bits1()
- {
- return Get_Bits(1);
- }
- /* advance by n bits */
- void Flush_Buffer(N)
- int N;
- {
- int Incnt;
- ld->Bfr <<= N;
- Incnt = ld->Incnt -= N;
- if (Incnt <= 24)
- {
- if (System_Stream_Flag && (ld->Rdptr >= ld->Rdmax-4))
- {
- do
- {
- if (ld->Rdptr >= ld->Rdmax)
- Next_Packet();
- ld->Bfr |= Get_Byte() << (24 - Incnt);
- Incnt += 8;
- }
- while (Incnt <= 24);
- }
- else if (ld->Rdptr < ld->Rdbfr+2044)
- {
- do
- {
- ld->Bfr |= *ld->Rdptr++ << (24 - Incnt);
- Incnt += 8;
- }
- while (Incnt <= 24);
- }
- else
- {
- do
- {
- if (ld->Rdptr >= ld->Rdbfr+2048)
- Fill_Buffer();
- ld->Bfr |= *ld->Rdptr++ << (24 - Incnt);
- Incnt += 8;
- }
- while (Incnt <= 24);
- }
- ld->Incnt = Incnt;
- }
- #ifdef VERIFY
- ld->Bitcnt += N;
- #endif /* VERIFY */
- }
- /* return next n bits (right adjusted) */
- unsigned int Get_Bits(N)
- int N;
- {
- unsigned int Val;
- Val = Show_Bits(N);
- Flush_Buffer(N);
- return Val;
- }