crc.h

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// ********************** START OF CRC.H **********************
//
// This header file contains the definitions for the two CRC 
// classes, Crc16 and Crc32.
//

#ifndef _CRC_DOT_H
#define _CRC_DOT_H

// The two CRC objects create 16 and 32 bit CRC values using the
// polynomials used by ZMODEM.  The calculations are table driven,
// with the table being initialized by the constructor at runtime.
// The constructor assigns an initial value to the crc, and then
// it is updated on a character by character basis.

class Crc32 {
    private :
        static unsigned long table[ 256 ];
        static int initialized;
        unsigned long crc;
    public :
        Crc32( unsigned long init_value );
        void update( int c );
        unsigned long value( void ){ return crc; }
};

inline void Crc32::update( int c )
{
    crc = table[ ( (int) crc ^ ( c & 0xff ) ) & 0xff ] ^
          ( ( crc >> 8 ) & 0x00FFFFFFL );
}

class Crc16 {
    private :
        static unsigned short table[ 256 ];
        static int initialized;
        unsigned short crc;
    public :
        Crc16( unsigned short init_value );
        void update( int c );
        unsigned short value( void ){ return crc; }
};

inline void Crc16::update( int c )
{
    crc = (unsigned short)
             ( table[ (( crc >> 8 ) & 0xff ) ] ^
               ( crc << 8 ) ^ ( c & 0xff ) );
}

#endif // #ifndef _CRC_DOT_H

// ************************ END OF CRC.H ************************