PndCRCCalculator calculates the CRC checksum from a given vector<char> More...

#include <PndCRCCalculator.h>

Inheritance diagram for PndCRCCalculator:

Public Member Functions
	PndCRCCalculator ()

	PndCRCCalculator (UInt_t order, ULong64_t polynom, ULong64_t CRCXor, UInt_t refIn, UInt_t refOut, UInt_t CRCInit_direct)

virtual	~PndCRCCalculator ()

ULong64_t	CalculateCRCTableFast (std::vector< char > p, ULong64_t len)

ULong64_t	ReflectBitsStream (ULong64_t crc, int bitnum)

void	PrintCRCTable ()

Protected Member Functions
void	GenerateCRCTable ()

Private Member Functions
	ClassDef (PndCRCCalculator, 1)

Private Attributes
const UInt_t	fOrder

const ULong64_t	fPolynom

const ULong64_t	fCRCXor

const UInt_t	fRefIn

const UInt_t	fRefOut

ULong64_t	fCRCMask

ULong64_t	fCRCHighBit

ULong64_t	fCRCInit_direct

ULong64_t	fCRCTab [256]

Detailed Description

PndCRCCalculator calculates the CRC checksum from a given vector<char>

PndCRCCalculator is based on a look-up table initially calculated from the paramters of the used CRC code. The output of the calculator was cross-checked with the online CRC calculator: http://www.sunshine2k.de/coding/javascript/crc/crc_js.html Both the generated look-up tables as the output match

Author: T.Stockmanns t.sto.nosp@m.ckma.nosp@m.nns@f.nosp@m.z-ju.nosp@m.elich.nosp@m..de

Definition at line 17 of file PndCRCCalculator.h.

Constructor & Destructor Documentation

PndCRCCalculator::PndCRCCalculator ( )

Definition at line 9 of file PndCRCCalculator.cxx.

References fCRCHighBit, fCRCMask, fOrder, and GenerateCRCTable().

                                    :
         fOrder(16), fPolynom(0x8005), fCRCXor(0x0000), fRefIn(0), fRefOut(0), fCRCInit_direct(0)
 {
         fCRCMask = ((((unsigned long)1<<(fOrder-1))-1)<<1)|1;
         fCRCHighBit = (unsigned long)1<<(fOrder-1);
 
         GenerateCRCTable();
 }

PndCRCCalculator::PndCRCCalculator	(	UInt_t	order,
		ULong64_t	polynom,
		ULong64_t	CRCXor,
		UInt_t	refIn,
		UInt_t	refOut,
		UInt_t	CRCInit_direct
	)

Definition at line 18 of file PndCRCCalculator.cxx.

References fCRCHighBit, fCRCMask, fOrder, and GenerateCRCTable().

                                                                                                                                         :
         fOrder(order), fPolynom(polynom), fCRCXor(CRCXor), fRefIn(refIn), fRefOut(refOut), fCRCInit_direct(CRCInit_direct)
 {
         fCRCMask = ((((unsigned long)1<<(fOrder-1))-1)<<1)|1;
         fCRCHighBit = (unsigned long)1<<(fOrder-1);
 
         GenerateCRCTable();
 }

PndCRCCalculator::~PndCRCCalculator ( )

virtual

Definition at line 28 of file PndCRCCalculator.cxx.

                                     {
         // TODO Auto-generated destructor stub
 }

Member Function Documentation

ULong64_t PndCRCCalculator::CalculateCRCTableFast	(	std::vector< char >	p,
		ULong64_t	len
	)

Definition at line 47 of file PndCRCCalculator.cxx.

References fCRCInit_direct, fCRCMask, fCRCTab, fCRCXor, fOrder, fRefIn, fRefOut, and ReflectBitsStream().

Referenced by CheckCRC().

                                                                                   {
 
         // fast lookup table algorithm without augmented zero bytes, e.g. used in pkzip.
         // only usable with polynom orders of 8, 16, 24 or 32.
 
         ULong64_t crc = fCRCInit_direct;
 
         std::vector<char>::iterator it = p.begin();
 
         if (fRefIn) {
                 crc = ReflectBitsStream(crc, fOrder);
         }
 
         if (!fRefIn) {
                 while (len--) {
                         crc = (crc << 8) ^ fCRCTab[((crc >> (fOrder - 8)) & 0xff) ^ (*it & 0xff)];
                         it++;
                 }
         } else {
                 while (len--) {
                         crc = (crc >> 8) ^ fCRCTab[(crc & 0xff) ^ (*it & 0xff)];
                         it++;
                 }
         }
         if (fRefOut ^ fRefIn) {
                 crc = ReflectBitsStream(crc, fOrder);
         }
         crc ^= fCRCXor;
         crc &= fCRCMask;
 
         return (crc);
 }

PndCRCCalculator::ClassDef	(	PndCRCCalculator	,
		1
	)

private

void PndCRCCalculator::GenerateCRCTable ( )

protected

Definition at line 80 of file PndCRCCalculator.cxx.

References fCRCHighBit, fCRCMask, fCRCTab, fOrder, fPolynom, fRefIn, i, and ReflectBitsStream().

Referenced by PndCRCCalculator().

                                         {
   // make CRC lookup table used by table algorithms
         ULong64_t bit, crc;
         for (int i=0; i<256; i++) {
                 crc=(ULong64_t)i;
                 if (fRefIn)
                   {
                     crc=ReflectBitsStream(crc, 8);
                   }
                 crc<<= fOrder-8;
 
                 for (int j=0; j<8; j++)
                   {
                         bit = crc & fCRCHighBit;
                         crc<<= 1;
                         if (bit)
                           {
                             crc^= fPolynom;
                           }
                   }
                 if (fRefIn)
                   {
                     crc = ReflectBitsStream(crc, fOrder);
                   }
                 crc&= fCRCMask;
                 fCRCTab[i]= crc;
         }
 }

void PndCRCCalculator::PrintCRCTable ( )

Definition at line 109 of file PndCRCCalculator.cxx.

References fCRCTab, and i.

 {
         for (int i = 0; i < 16; i++){
                 for (int j = 0; j < 16; j++){
                         std::cout << std::hex << fCRCTab[i*16 + j] << " ";
                 }
                 std::cout << std::endl;
         }
 }

ULong64_t PndCRCCalculator::ReflectBitsStream	(	ULong64_t	crc,
		int	bitnum
	)

Definition at line 119 of file PndCRCCalculator.cxx.

References i.

Referenced by CalculateCRCTableFast(), and GenerateCRCTable().

                                                                        {
 
         // reflects the lower 'bitnum' bits of 'crc'
 
         ULong64_t i, j=1, crcout=0;
 
         for (i=(ULong64_t)1<<(bitnum-1); i; i>>=1)
           {
                 if (crc & i)
                   {
                     crcout|=j;
                   }
                 j<<= 1;
           }
         return (crcout);
 }