/*=============================================================================
|
| NAME
|  
|     crcCode.h
|
| DESCRIPTION
|  
|     Class definition for CRCCode
|
| AUTHOR
|
|      Sean O'Connor
|    
| LEGAL
|
|     CRCDemo Version 2.1 - A Program for generating and checking CRC codes.
|     Copyright (C) 1999-2008 by Sean Erik O'Connor.  All Rights Reserved.
|
|     This program is free software; you can redistribute it and/or
|     modify it under the terms of the GNU General Public License
|     as published by the Free Software Foundation;  version 2
|     of the License.
|     
|     This program is distributed in the hope that it will be useful,
|     but WITHOUT ANY WARRANTY; without even the implied warranty of
|     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
|     GNU General Public License for more details.
|     
|     You should have received a copy of the GNU General Public License
|     along with this program; if not, write to the Free Software
|     Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
|     
|     The author's address is artifex@seanerikoconnor.freeservers.com
|
+============================================================================*/


/*=============================================================================
|
| NAME
|  
|    CRCCode     
|
| DESCRIPTION
|  
|    Class for CRC (Cyclic Redundancy Check) code encoding and 
|    decoding.
|
| METHOD
|
|    Encoding (systematic):
|
|      c( x ) = m( x ) + p( x )
|
|                  n-k
|      m( x ) =  x     i( x )             Message portion of codeword c(x).
|                  n-k
|      p( x ) = -x     i( x ) mod g( x )  Parity portion of codeword c(x).
|
|    Decoding:
|
|      s( x ) = c( x ) mod g( x )         Syndrome of codeword c(x).
|
|      The shift register computes
|
|          n-k
|      [ x     c( x ) ] mod g( x )
|
|      This shifted syndrome is OK to use for error checking because it 
|      is zero iff c( x ) was a codeword.
|
+============================================================================*/

class CRCCode
{
    public:
		// Construct CRC from given generator polynomial.
        CRCCode( char *                              g, 
			     unsigned long shiftRegisterPreset = 0L,
				 bool          invertParity        = false ) ;

		~CRCCode() ;

		// Return the parity bits computed on the data in the buffer.
        // Parity bits are in the most significant bits of the buffer.
		unsigned long int parityBits( unsigned char * buffer, long int n ) ;

        // Append CRC parity bytes to the end of the buffer.
		// The buffer must be long enough to accomodate the
		// extra parity bits.  Buffer length is increased
		// upon exit.
        void addParityToBuffer( unsigned char * buffer, long int n ) ;

        // Compute the shifted syndrome of the codeword.
		// Zero indicates we have a codeword.
		unsigned long int shiftedSyndrome( unsigned char * buffer, 
				                           long int        n ) ;

		// Return the number of parity bytes.
		int getNumParityBytes( void ) const ;

	private:
		// The linear feedback shift register circuit we will use
		// to do all the computations.
		ShiftRegister shiftRegister_ ;

		// Number of parity bits, n - k
		int numParityBits_ ;

		// Shift register may be loaded with a value
		// (usually FFF..FFF) instead of zero.
		int shiftRegisterPreset_ ;

		// Some implementations do a 1's complement
		// of the parity bits.
		bool invertParity_ ;

	private:
		// Disable automatic generation of copy constructor
		// and assignment operator.
		CRCCode( const CRCCode & ) ;
		CRCCode operator=( const CRCCode & ) ;
} ;