Month

Brief Information about the May 99 CSIG Meeting

A Review of the C Users Journal, 6/99, on CRC Calculations

Author: Colin Mahoney

CRC: A Paper On CRCs

This CRC web was created because of the popularity of a paper on CRC algorithms written by Ross Williams and posted to some Internet newsgroups on 19 August 1993. This paper is available by FTP as a pure text file. It can also be browsed directly on the web:

• ftp://ftp.rocksoft.com/clients/rocksoft/papers/crc_v3.txt.
• http://www.paranoia.com/~filipg/HTML/LINK/F_crc_v3.html.

Here is the title and abstract of the paper:

A Painless Guide to CRC Error Detection Algorithms

This document explains CRCs (Cyclic Redundancy Codes) and their table-driven implementations in full, precise detail. Much of the literature on CRCs, and in particular on their table-driven implementations, is a little obscure. This document is an attempt to provide a clear and simple no-nonsense explanation of CRCs and to absolutely nail down every detail of the operation of their high-speed implementations. In addition to this, this document presents a parameterized model CRC algorithm called the "Rocksoft^tm Model CRC Algorithm". The model algorithm can be parameterized to behave like most of the CRC implementations around, and so acts as a good reference for describing particular algorithms. A low-speed implementation of the model CRC algorithm is provided in the C programming language. Lastly there is a section giving two forms of high-speed table driven implementations, and providing a program that generates CRC lookup tables.

// Listing 2	    ( from C Users Journal, June 1999 )
//
// Author: Colin Mahoney (cmahoney@readysoft.es)
//
//      /link setargv.obj  req'd for wildcard handling in Microsoft VC++ (b.arnold)
//
 
#include <iostream>
#include <fstream>
#include <iterator>

using namespace std;
#include "crc.h"

int main( int argc, char* argv[] )
    {
    if( argc < 2 )
	{
	cerr << "Usage: CRC16 file1 file2...\n";
	return 1;
	}

    typedef cdm_crc::CRCGenerator<16, 0x8005, 0, 0, true> CRC16;
    CRC16 crc16;
    cout.setf( ios_base::hex, ios_base::basefield );
    cout.setf( ios_base::showbase );
    for( int i = 1; i < argc; i++ )
	{
	ifstream infile( argv[i] );
	infile.unsetf( ios_base::skipws );
	if( !infile )
	    {
	    cerr << "Error: unable to open " << argv[i] << '\n';
	    continue;
	    }
	crc16.Process( istream_iterator<unsigned char>( infile ),
	istream_iterator<unsigned char>() );
	unsigned long ncrcVal = crc16.GetNormalCRC();
	ncrcVal >>= (cdm_crc::CRCMaxBits-crc16.GetWidth() );
	cout << "File: " << argv[i] << '\t' << 
	"CRC-16 checksum: " << ncrcVal << '\n';
	}
    return 0;
    }

SOURCE CODE

Source Code Files