crc32.cpp

QAM module to use in Java with an easy interface and powerful performance

//---------------------------------------------------------------------------


#pragma hdrstop

#include "Crc32.h"
#include "main.h"

//---------------------------------------------------------------------------

#pragma package(smart_init)



// define static member

FastCrc::Table FastCrc::_table;

void FastCrc::Table::Init (Crc::Type key)
{
	assert (key != 0);
	if (key == _key)
		return;
	_key = key;

        //Application->MessageBox("This should be on top.", "Look", MB_OK);

	// for all possible byte values
	for (unsigned i = 0; i < 256; ++i)
	{
		Crc::Type reg = i << 24;
		// for all bits in a byte
		for (int j = 0; j < 8; ++j)
		{
			bool topBit = (reg & 0x80000000) != 0;
			reg <<= 1;
			if (topBit)
				reg ^= _key;
		}
		_table [i] = reg;
	}
}

void FastCrc::PutByte (unsigned byte)
{
	unsigned top = _register >> 24;
	top ^= byte;
	_register = (_register << 8) ^ _table [top];
}
/*
int main ()
{
	std::string msg ("Harry had a little lamp");
	std::string exMsg (msg);
	exMsg.resize (msg.length () + 4);

	Crc::Type const ethernetKey = 0x04c11db7;

	FastCrc fastCrc (ethernetKey);

	for (int i = 0; i < msg.length (); ++i)
	{
		fastCrc.PutByte (msg [i]);
	}
	Crc::Type newCrc = fastCrc.Done ();
	std::cout << "\n0x" << std::hex << newCrc << std::endl;

	return 0;
}
 */


void SlowCrc::PutBit (bool bit)
{
  //  std::cout << bit? "1": "0";

    bool topBit = (_register & 0x80000000) != 0;
    // shift bit into register from the right
    _register <<= 1;
    _register ^= (bit? 0x1: 0x0); // OR or XOR, same result
    if (topBit)
    {
        // XOR the 32-bits of the key.
        // The implicit high bit of the 33-bit key conceptually
        // clears the topBit shifted out of the register
        _register ^= _key;
    }
}


unsigned long __fastcall FastCrc::CalcCRC32(unsigned char * Buf, int Size)
{
        unsigned long crc32;
        for(int i=0;i<(Size);i++)PutByte(Buf[i]);
        crc32=Done();
        return crc32;
}