Error Detection Based on Check Digit Schemes

// checksum5.cpp
//
#include "stdafx.h"

#include <iostream>
#include <string>
#include <assert.h>

#include "convert.h"

// Multiplicative Table
unsigned int
M[10][10] = { {0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
              {1, 2, 3, 4, 0, 6, 7, 8, 9, 5},
              {2, 3, 4, 0, 1, 7, 8, 9, 5, 6},
              {3, 4, 0, 1, 2, 8, 9, 5, 6, 7},
              {4, 0, 1, 2, 3, 9, 5, 6, 7, 8},
              {5, 9, 8, 7, 6, 0, 4, 3, 2 ,1},
              {6, 5, 9, 8, 7, 1, 0, 4, 3, 2},
              {7, 6, 5, 9, 8, 2, 1, 0, 4, 3},
              {8, 7, 6, 5, 9, 3, 2, 1, 0, 4},
              {9, 8, 7, 6, 5, 4, 3, 2, 1, 0} };

// Position Table
//   Note: Repeats after 8 Rows...
unsigned int
P[8][10] = { {0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
             {1, 5, 7, 6, 2, 8, 3, 0, 9, 4},
             {5, 8, 0, 3, 7, 9, 6, 1, 4, 2},
             {8, 9, 1, 6, 0, 4, 3, 5, 2, 7},
             {9, 4, 5, 3, 1, 2, 6, 8, 7, 0},
             {4, 2, 8, 6, 5, 7, 3, 9, 0, 1},
             {2, 7, 9, 3, 8, 0, 6, 4, 1, 5},
             {7, 0, 4, 6, 9, 1, 3, 2, 5, 8} };

// Inverse Table
unsigned int
Inv[] = {0, 4, 3, 2, 1, 5, 6, 7, 8, 9};



int main(int argc, char* argv[])
{

    // Check digit should be 7
    //   Bressoud and Wagon appear to be wrong
    //   in Computational Number Theory, p. 162
    // CNT claims c = 4, Inv( c ) = 1???
    // _tstring number = _T("1793");

    // Check digit should be 0
    //   See http://www.answers.com/topic/verhoeff-algorithm
    // _tstring number = _T("1428570");

    // Check digit should be 8
    //   See http://www.esb.ie/esbnetworks/mrso/mprn.jsp
    _tstring number = _T("1000372996");


    _tcout << _T("number: ") << number << endl;

    // It's too bad we had to toss out the
    //   const_reverse_iterator to get this to compile...
    // Also, M$ will only give you the ASCII number to the
    //   TCHAR if: _tcout << *it;
    int i = 0, c = 0;
    for( _tstring::reverse_iterator it = number.rbegin();
                                     it != number.rend(); it++, i++)
    {
        // Consume non digits
        while( it != number.rend() && false == isdigit( *it ) ) { it++; }
        if( it == number.rend() ) { break; }

        // c = M[ c ][ P[ i % 8 ][ CharToNumber( *it ) ]];
        unsigned int n = CharToNumber( *it );
        unsigned int p = P[ i % 8 ][ n ];
                     c = M[ c ][ p ];        
     
    }

    c = Inv[ c ];

    _tcout << _T("check digit is: ") << c << endl;

    return 0;
}