bitstrm.cpp

EM8511s中使用的mpg播放器

#include "bitstrm.h"

// this class will increment Err if you proceed past the end of the buffer
BitStream::BitStream (unsigned char *pBuffer, unsigned long Length, int *Err)
{
	m_rdbfr = pBuffer;
	m_rdbfr_length = Length;
	m_nbits = 0;
	initbits (Err);
}

BitStream::~BitStream ()
{
}
			   
void BitStream::initbits (int *Err)
{
	m_incnt = 0;
	m_rdptr = m_rdbfr + m_rdbfr_length;
	m_rdmax = m_rdptr;
	m_bitcnt = 0;
	m_bfr = 0;
	m_rdptr = m_rdbfr;
	flushbits (0, Err);
}

// return next n bits (right adjusted) without advancing
unsigned int BitStream::showbits (int n)
{
	return m_bfr >> (32-n);
}

// advance by n bits
void BitStream::flushbits (int n, int *Err)
{
	int incnt;

	m_nbits += n;

	if (n == 32)
		m_bfr = 0;
	else
		m_bfr <<= n;	
	incnt = m_incnt -= n;
	if (incnt <= 24)
	{
		if (m_rdptr < m_rdbfr+(m_rdbfr_length-4))
		{
			do
			{
				m_bfr |= *m_rdptr++ << (24 - incnt);
				incnt += 8;
			}
			while (incnt <= 24);
		}
		else
		{
			do
			{
				if (m_rdptr >= m_rdbfr+m_rdbfr_length)
				{
					*Err++;
					m_bfr |= 0 << (24 - incnt);
				}
				else
					m_bfr |= *m_rdptr++ << (24 - incnt);
				incnt += 8;
			}
			while (incnt <= 24);
		}
		m_incnt = incnt;
	}
}

void BitStream::flushbits32 (int *Err)
{
	int incnt;

	m_nbits += 32;

	m_bfr = 0;
	incnt = m_incnt;
	incnt -= 32;
    while (incnt <= 24)
    {
		if (m_rdptr >= m_rdbfr+m_rdbfr_length)
		{
			*Err++;
			m_bfr |= 0 << (24 - incnt);
		}
		else
			m_bfr |= *m_rdptr++ << (24 - incnt);
		incnt += 8;
    }
	m_incnt = incnt;
}


// return next n bits (right adjusted)
unsigned int BitStream::getbits (int n, int *Err)
{
	unsigned int l;

	l = showbits (n);
	flushbits (n, Err);

	return l;
}

unsigned int BitStream::getbits32 (int *Err)
{
	unsigned int l;

	l = showbits (32);
	flushbits32 (Err);

	return l;
}

void BitStream::align (int *Err)
{
	int incnt;

	if (m_incnt != 32)
	{
		incnt = m_incnt % 8;
		flushbits (incnt, Err);
	}
}

long BitStream::getnbits ()
{
	return m_nbits;
}