bits.cpp

来自「Motion JPEG编解码器源代码」· C++ 代码 · 共 503 行

/** @file bits.cc, bit-level output                                              */

/* Copyright (C) 2001, Andrew Stevens <[e-mail]> *

 *
 * 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 <config.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <assert.h>
#include "mjpeg_logging.h"
#include "bits.hpp"


const unsigned int BitStreamBuffering::BUFFER_SIZE = 64 * 1024;
const unsigned int BitStreamBuffering::BUFFER_CEILING = 32 * 1024 * 1024;

BitStreamBuffering::BitStreamBuffering() :
    bfr(0),
    bfr_size(0),
    buffered(0)
    
{
}


/*****
 *
 * Pseudo-destructor. Frees the internal buffer and marks buffer as
 * empty.
 *
 *****/
void BitStreamBuffering::Release()
{
    if( bfr != 0)
        delete bfr;
    bfr = 0;
    bfr_size = 0;
    buffered = 0;
}


/*****
 *
 * Empty the buffer.
 *
 *****/

void BitStreamBuffering::Empty()
{
    buffered = 0;
}

/** sets the internal buffer size. 
    @param new_buf_size requests new internal buffer size 
*/
void BitStreamBuffering::SetBufSize( unsigned int new_buf_size)
{
    //
    // If size has changed and we won't lose buffered data
    // we adjust the buffer size, otherwise we ignore the request
    //
	if( new_buf_size > BUFFER_CEILING )
	{
		mjpeg_error_exit1("INTERNAL ERROR: additional data required but "
                          " input buffer size would exceed ceiling");
	}
    
    if( new_buf_size > buffered && bfr_size != new_buf_size )
	{
		uint8_t *new_buf = new uint8_t[new_buf_size];
		memcpy( new_buf, bfr, static_cast<size_t>(buffered) );
        if( bfr != 0 )
            delete [] bfr;
		bfr_size = new_buf_size;
		bfr = new_buf;
	}

}

/****************************
 *
 * Return the pointer to where (after, if necessary extending the
 * buffer) up to to_append bytes may be appended to the buffered bytes
 *
 ****************************/

uint8_t *BitStreamBuffering::StartAppendPoint( unsigned int to_append )
{
    unsigned int resize_size = bfr_size;
    assert( resize_size != 0 );
    while( resize_size - buffered < to_append )
    {
        resize_size *= 2;
    }
    if( resize_size != bfr_size )
        SetBufSize( resize_size );
    return bfr+buffered;
}

/**
   Refills an IBitStream's input buffer based on the internal
   variables buffered and bfr_size.
   Strategy: we read 1/4 of a buffer, always.
 */
bool IBitStream::ReadIntoBuffer(unsigned int to_read)
{
	size_t i;
    unsigned int read_pow2 = BUFFER_SIZE/4;
    while( read_pow2 < to_read ) 
        read_pow2 <<= 1;


    i = ReadStreamBytes( StartAppendPoint(read_pow2), 
                         static_cast<size_t>(read_pow2) );      
	//i = fread(StartAppendPoint(read_pow2), sizeof(uint8_t), 
    //			  static_cast<size_t>(read_pow2), fileh);
    Appended(static_cast<unsigned int>(i));

	if ( i == 0 )
	{
		eobs = true;
		return false;
	}
	return true;
}




#define masks(idx) (1<<(idx))

/*read 1 bit from the bit stream 
@returns the read bit, 0 on EOF */
uint32_t IBitStream::Get1Bit()
{
	unsigned int bit;

	if (eobs)
		return 0;

	bit = (bfr[byteidx] & masks(bitidx - 1)) >> (bitidx - 1);
	bitreadpos++;
	bitidx--;
	if (!bitidx)
	{
		bitidx = 8;
		byteidx++;
		if (byteidx == buffered)
		{
			ReadIntoBuffer();
		}
	}

	return bit;
}

/*read N bits from the bit stream 
@returns the read bits, 0 on EOF */
uint32_t IBitStream::GetBits(int N)
{
	uint32_t val = 0;
	int i = N;
	unsigned int j;

	// Optimize: we are on byte boundary and want to read multiple of bytes!
	if ((bitidx == 8) && ((N & 7) == 0))
	{
		i = N >> 3;
		while (i > 0)
		{
			if (eobs)
				return 0;
			val = (val << 8) | bfr[byteidx];
			byteidx++;
			bitreadpos += 8;
			if (byteidx == buffered)
			{
				ReadIntoBuffer();
			}
			i--;
		}
	}
	else
	{
		while (i > 0)
		{
			if (eobs)
				return 0;

			j = (bfr[byteidx] & masks(bitidx - 1)) >> (bitidx - 1);
			bitreadpos++;
			bitidx--;
			if (!bitidx)
			{
				bitidx = 8;
				byteidx++;
				if (byteidx == buffered)
				{
					ReadIntoBuffer();
				}
			}
			val = (val << 1) | j;
			i--;
		}
	}
	return val;
}


/** This function seeks for a byte aligned sync word (max 32 bits) in the bit stream and
    places the bit stream pointer right after the sync.
    This function returns 1 if the sync was found otherwise it returns 0
@param sync the sync word to search for
@param N the number of bits to retrieve
@param lim number of bytes to search through
@returns false on error */

bool IBitStream::SeekSync(uint32_t sync, int N, int lim)
{
	uint32_t val, val1;
	uint32_t maxi = ((1U<<N)-1); /* pow(2.0, (double)N) - 1 */;
	if( maxi == 0 )
	{
		maxi = 0xffffffff;
	}
	while (bitidx != 8)
	{
		Get1Bit();
	}

	val = GetBits(N);
	if( eobs )
		return false;
	while ((val & maxi) != sync && --lim)
	{
		val <<= 8;
		val1 = GetBits( 8 );
		val |= val1;
		if( eobs )
			return false;
	}
  
	return (!!lim);
}

/****************
 *
 * Move the bit read position forward a specified number of bytes
 * buffering bytes skipped over that are not already buffered
 *
 ***************/

void IBitStream::SeekFwdBits( unsigned int bytes_to_seek_fwd)
{ 
    assert(bitidx == 8);
    unsigned int req_byteidx = byteidx + bytes_to_seek_fwd;
    while( req_byteidx >= buffered && !eobs)
    {
        ReadIntoBuffer( req_byteidx - (buffered-1) );
    }
    
    eobs = ( req_byteidx >= buffered );
    if( eobs )
        bitreadpos += (buffered - byteidx)*8;
    else
        bitreadpos += bytes_to_seek_fwd*8;
    byteidx = req_byteidx;
}


/**
  Flushes all read input up-to *but not including* byte flush_upto.
  @param flush_to the number of bits to flush
*/

void IBitStream::Flush(bitcount_t flush_upto )
{
	if( flush_upto > bfr_start+buffered )
		mjpeg_error_exit1("INTERNAL ERROR: attempt to flush input beyond buffered amount" );

	if( flush_upto < bfr_start )
		mjpeg_error_exit1("INTERNAL ERROR: attempt to flush input stream before  first buffered byte %lld last is %lld", flush_upto, bfr_start );

	unsigned int bytes_to_flush = 
		static_cast<unsigned int>(flush_upto - bfr_start);
	//
	// Don't bother actually flushing until a good fraction of a buffer
	// will be cleared.
	//

	if( bytes_to_flush < bfr_size/2 )
		return;
	buffered -= bytes_to_flush;
	bfr_start = flush_upto;
	byteidx -= bytes_to_flush;
	memmove( bfr, bfr+bytes_to_flush, static_cast<size_t>(buffered));
}


/**
  Undo scanning / reading
  N.b buffer *must not* be flushed between prepareundo and undochanges.
  @param undo handle to store the undo information
*/
void IBitStream::PrepareUndo( IBitStreamUndo &undo)
{
	undo = *(static_cast<IBitStreamUndo*>(this));
}

/**
Undoes changes committed to an IBitStream. 
@param undo handle to retrieve the undo information   
 */
void IBitStream::UndoChanges( IBitStreamUndo &undo)
{
	*(static_cast<IBitStreamUndo*>(this)) = undo;
}

/**
   Read a number bytes over an IBitStream, using the buffer. 
   @param dst buffer to read to 
   @param length the number of bytes to read
 */
unsigned int IBitStream::GetBytes(uint8_t *dst, unsigned int length)
{
	unsigned int to_read = length;
	if( bytereadpos < bfr_start)
		mjpeg_error_exit1("INTERNAL ERROR: access to input stream buffer @ %lld: before first buffered byte (%lld)", bytereadpos, bfr_start );

	if(  bytereadpos+length > bfr_start+buffered )
	{
		if( !EndOfStream() )
        {
			mjpeg_error("INTERNAL ERROR: access to input stream buffer beyond last buffered byte @POS=%lld END=%d REQ=%lld + %d bytes", 
                        bytereadpos,
                        buffered, 
                        bytereadpos-bfr_start,
                        length  );
            abort();
        }
		to_read = static_cast<unsigned int>( (bfr_start+buffered)- bytereadpos );
	}
	memcpy( dst, 
			bfr+(static_cast<unsigned int>( bytereadpos-bfr_start)), 
			to_read);
	// We only ever flush up to the start of a read as we
	// have only scanned up to a header *beginning* a block that is then
	// read
	//flush( bytereadpos );
	bytereadpos += to_read;
	return to_read;
}


#ifdef REDUNDANT_CODE
/**
   Initialize buffer, call once before first putbits or alignbits.
  @param bs_filename output filename
  @param buf_size size of the temporary output buffer to use
*/
void OBitStream::open(char *bs_filename, unsigned int buf_size)
{
	if ((fileh = fopen(bs_filename, "wb")) == NULL)
	{
		mjpeg_error_exit1( "Unable to open file %s for writing; %s", 
						   bs_filename, strerror(errno));
	}
	filename = strcpy( new char[strlen(bs_filename)+1], bs_filename );
    SetBufSize(buf_size);
	// Save multiple buffering...
	setvbuf(fileh, 0, _IONBF, 0 );
	bitidx = 8;
	byteidx = 0;
	bitwritepos = 0LL;
	outbyte = 0;
}


/** 
    Closes the OBitStream. Flushes the output buffer and closes the output file if one was open. 
 */
void OBitStream::close()
{
	if (fileh)
	{
		if (byteidx != 0)
			fwrite(bfr, sizeof(uint8_t), byteidx, fileh);
		fclose(fileh);
		delete filename;
		fileh = NULL;
	}
}

/**
  Puts a byte into the OBitStream.  Puts the byte into the internal
  buffer; if the buffer is full, it flushes the buffer to disk.
 */
void OBitStream::putbyte()
{
    bfr[byteidx++] = outbyte;
    if (byteidx == bfr_size)
    {
		if (fwrite(bfr, sizeof(uint8_t), bfr_size, fileh) != bfr_size)
			mjpeg_error_exit1( "Write failed: %s", strerror(errno));
		byteidx = 0;
    }
	bitidx = 8;
}

/** write rightmost n (0<=n<=32) bits of val to outfile 
@param val value to write bitwise
@param n number of bits to write
*/
void OBitStream::putbits(uint32_t val, int n)
{
	int i;
	unsigned int mask;

    bitwritepos += n;
    while( n >= bitidx )
    {
        outbyte = 
            (outbyte<<bitidx) | ((val >> (n-bitidx)) & ((1u<<bitidx)-1));
        n -= bitidx;
        putbyte();
    }
    if( n > 0 )
    {
        bitidx -= n;
        outbyte = val & ((1u<<bitidx)-1);
    }
#ifdef ORIGINAL
	mask = 1 << (n - 1); /* selects first (leftmost, msb) bit */
	for (i = 0; i < n; i++)
	{
		bitwritepos += 1;
		outbyte <<= 1;
		if (val & mask)
			outbyte |= 1;
		mask >>= 1; /* select next bit */
		bitidx--;
		if (bitidx == 0) /* 8 bit buffer full */
			putbyte();
	}
#endif
}

/** write rightmost bit of val to outfile
    @param val value to write one bit of
*/
void OBitStream::put1bit(int val)
{
	++bitwritepos;
    outbyte = (outbyte<<1) | (val & 0x1);
	--bitidx;
	if (bitidx == 0) /* 8 bit buffer full */
		putbyte();
}


/** zero bit stuffing to next byte boundary (5.2.3, 6.2.1) */
void OBitStream::alignbits()
{
	if (bitidx != 8)
		putbits( 0, bitidx);
    flush_bytes();
}

#endif

/* 
 * Local variables:
 *  c-file-style: "stroustrup"
 *  tab-width: 4
 *  indent-tabs-mode: nil
 * End:
 */