getbit.c

DVD转换到AVI的源代码

/* 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 "global.h"
#include "getbit.h"

__forceinline static unsigned int Get_Short(void);

void Initialize_Buffer()
{
	Rdptr = Rdbfr + BUFFER_SIZE;
	Rdmax = Rdptr;

	if (SystemStream_Flag)
	{
		if (Rdptr >= Rdmax)
			Next_Packet();
		CurrentBfr = *Rdptr++ << 24;

		if (Rdptr >= Rdmax)
			Next_Packet();
		CurrentBfr += *Rdptr++ << 16;

		if (Rdptr >= Rdmax)
			Next_Packet();
		CurrentBfr += *Rdptr++ << 8;

		if (Rdptr >= Rdmax)
			Next_Packet();
		CurrentBfr += *Rdptr++;

		Fill_Next();
	}
	else
	{
		Fill_Buffer();

		CurrentBfr = (*Rdptr << 24) + (*(Rdptr+1) << 16) + (*(Rdptr+2) << 8) + *(Rdptr+3);
		Rdptr += 4;

		Fill_Next();
	}

	BitsLeft = 32;
}

unsigned int Get_Bits_All(unsigned int N)
{
	N -= BitsLeft;
	Val = (CurrentBfr << (32 - BitsLeft)) >> (32 - BitsLeft);

	if (N != 0)
		Val = (Val << N) + (NextBfr >> (32 - N));

	CurrentBfr = NextBfr;
	BitsLeft = 32 - N;
	Fill_Next();

	return Val;
}

void Flush_Buffer_All(unsigned int N)
{
	CurrentBfr = NextBfr;
	BitsLeft = BitsLeft + 32 - N;
	Fill_Next();
}

void Next_Packet()
{
	static unsigned int code, Packet_Length, Packet_Header_Length;

	for (;;)
	{
		code = Get_Short();
		code = (code<<16) + Get_Short();

		// remove system layer byte stuffing
		while ((code & 0xffffff00) != 0x00000100)
			code = (code<<8) + Get_Byte();

		switch (code)
		{
			case PACK_START_CODE:
				Rdptr += 8;
				break;

			case VIDEO_ELEMENTARY_STREAM:   
				Packet_Length = Get_Short();
				Rdmax = Rdptr + Packet_Length;

				code = Get_Byte();

				if ((code & 0xc0)==0x80)
				{
					code = Get_Byte();
					Packet_Header_Length = Get_Byte();

					Rdptr += Packet_Header_Length;
					return;
				}
				else
					Rdptr += Packet_Length-1;
				break;

			default:
				if (code>=SYSTEM_START_CODE)
				{
					code = Get_Short();
					Rdptr += code;
				}
				break;
		}
	}
}

void Fill_Buffer()
{
	Read = _read(Infile[File_Flag], Rdbfr, BUFFER_SIZE);

	if (Read < BUFFER_SIZE)
		Next_File();

	Rdptr = Rdbfr;

	if (SystemStream_Flag)
		Rdmax -= BUFFER_SIZE;
}

static unsigned int Get_Short()
{
	unsigned int i = Get_Byte();
	return (i<<8) + Get_Byte();
}

void Next_File()
{
	if (File_Flag < File_Limit-1)
		File_Flag ++;

	_lseeki64(Infile[File_Flag], 0, SEEK_SET);
	_read(Infile[File_Flag], Rdbfr + Read, BUFFER_SIZE - Read);
}