/* +++Date last modified: 05-Jul-1997 */ /**************************************************************************** * @(#)MODULUS.c * @(#)- Basic routines for creating and checking modulus values * * ***************************************************************************** * CONTENTS: * * modulus10() ; Returns the modulus 10 check digit. * modulus11() ; Returns the modulus 11 check digit * check_modulus10() ; Checks if the check digit in string is correct * check_modulus11() ; Checks if the check digit in string is correct * ***************************************************************************** * DESCRIPTION: * * Calculations of modulus 10 check digits: * * Multiply units position an every Base 6 1 2 4 8 * alternate position i basic code 6 2 8 * number by 2, starting from righthand * digit = 1256 * * Bring down digits that were not 1 4 * multiplied by 2 * * Cross add these digits to digits in * first product 1+2+5+6+1+4 = 19 * * Enter next higher number with a ending * zero. If the number already ends with * zero keep it. 20 * * Subtract the cross add sum with next * higher and you've got the check digit 20 - 19 = 1 * Í * Result : 61248 1 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Calculations of modulus 11 check digits: * * Assigned weighted checking factor base 9 4 3 4 5 7 8 4 2 * to each digits position of basic weight 4 3 2 7 6 5 4 3 2 * code number starting with units * position of number and progressing * to most significant digit * * Weight used is: * 765432765432765432765432765432765432 etc. * * Multiply esch digit of the basic 36 * code number by its weighted checking 12 * factor, and add the products 6 * 28 * 30 * 35 * 32 * 12 * 4 * * * Sum = 195 * * Divide Sum of products by 11 195 % 11 = 17 plus remainder of 8 * * Subtract remainder from 11 11 - 8 = 3 * difference is check digit Í * * Result : 943457842 3 * ***************************************************************************** *@(#)1993 Erik Bachmann (E-mail: ebp@dde.dk) * * Released to public domain 27-Oct-95 *****************************************************************************/ #include /* pow() */ #include /* strlen(), strncpy() */ #include "bacstd.h" /* /-------------------------------------\ | MODULUS10 |------------------------------------| |\-------------------------------------/ | | |----------------------------------------------------------------------------| | CALL: | iMod10 = modulus10("61248") ; | | HEADER: | math.h pow() | | GLOBALE VARIABLES: | % | | ARGUMENTS: | char *pszBase | The string on which the modulus is performed | | | PROTOTYPE: | int _CfnTYPE modulus10(char *pszBase) ; | | RETURN VALUE: | int Modulus value | | MODULE: | modulus.c |----------------------------------------------------------------------------| | | |----------------------------------------------------------------------------| |1993-09-29/Erik Bachmann \---------------------------------------------------------------------------|*/ int _CfnTYPE modulus10(char *pszBase) { int iSum = 0, iTemp = 0, i, j ; /*--------------------------------*/ /* Get units position an every alternate position i basic code, starting from righthand and cross add */ for (i = strlen(pszBase) - 1, j = 0 ; i >= 0 ; i -= 2, j++ ) { iSum += (pszBase[i] - '0') * (int)pow(10, j) ; } iSum *= 2 ; /* Multiply by 2 */ iTemp = iSum ; /* Bring down digits that were not multiplied by 2 */ for ( iSum = 0 ; j >= 0 ; j--) { iSum += iTemp % 10 ; /* Cross add these digits to digits in first product */ iTemp /= 10 ; } /* Enter next higher number with a ending zero. If the number already ends with zero keep it. */ for (i = strlen(pszBase) - 2 ; i >= 0 ; i -= 2 ) { iSum += (pszBase[i] - '0') ; } /* Subtract the cross add sum with next higher and you've got the check digit*/ if ( (iSum % 10) != 0) { iSum = ( ( (iSum / 10) + 1 ) * 10) - iSum ; } else iSum = 0 ; return( iSum ) ; } /*** modulus10() ***/ /* /-------------------------------------\ | MODULUS11 |------------------------------------| |\-------------------------------------/ | | |----------------------------------------------------------------------------| | CALL: | iMod11 = modulus11("943457842") ; | | HEADER: | math.h pow() | | GLOBALE VARIABLES: | % | | ARGUMENTS: | char *pszBase | The string on which the modulus is performed | | PROTOTYPE: | int _CfnTYPE modulus11(char *pszBase) ; | | RETURN VALUE: | int Modulus value | | MODULE: | modulus.c |----------------------------------------------------------------------------| | | |----------------------------------------------------------------------------| |1993-09-29/Erik Bachmann \---------------------------------------------------------------------------|*/ int _CfnTYPE modulus11(char *pszBase) { char *pszWeids = "765432" ; int iSum = 0 ; int i, j ; /*--------------------------*/ /* Assigned weighted checking factor to each digits position of basic code number starting with units position of number and progressing to most significant digit */ for ( i = strlen(pszBase) - 1, j = 5 ; i >= 0 ; i-- ) { /* Multiply esch digit of the basic code number by its weighted checking factor, and add the products */ iSum += (pszBase[i] - '0') * (pszWeids[j--] - '0') ; if (j < 0) j = 5 ; } /* Divide Sum of products by 11 Subtract remainder from 11 difference is check digit */ iSum = 11 - (iSum % 11) ; return( iSum ) ; } /*** modulus11() ***/ /*--------------------------------------------------------------*/ /* /-------------------------------------\ | CHECK_MODULUS10 |------------------------------------| |\-------------------------------------/ | | |----------------------------------------------------------------------------| | CALL: | iMod10 = check_modulus10("612481") ; | | HEADER: | math.h pow() | | GLOBALE VARIABLES: | % | | ARGUMENTS: | char *pszBase | The string including the digit to be checked | | | PROTOTYPE: | int _CfnTYPE check_modulus10(char *pszBase) ; | | RETURN VALUE: | int 0 = OK | else value - 10 = correct digit | MODULE: | modulus.c |----------------------------------------------------------------------------| | | |----------------------------------------------------------------------------| |1993-09-29/Erik Bachmann \---------------------------------------------------------------------------|*/ int _CfnTYPE check_modulus10(char *pszBase) { char szTmp[11] ; int iTmp = 0 ; /*--------------------*/ strncpy(szTmp, pszBase, strlen(pszBase) - 1) ; szTmp[strlen(pszBase) - 1] = '\0' ; /* Extract base */ iTmp = pszBase[strlen(pszBase) - 1] - '0' ; /* Extract current check digit */ if ( modulus10(szTmp) == iTmp ) return( 0 ) ; /* Check digit is OK */ else return( 10 + modulus10(szTmp) ) ;/* On error return the correct + 10 */ } /*** check_modulus10() ***/ /*--------------------------------------------------------------*/ /* /-------------------------------------\ | CHECK_MODULUS11 |------------------------------------| |\-------------------------------------/ | | |----------------------------------------------------------------------------| | CALL: | iMod11 = check_modulus11("9434578423") ; | | HEADER: | math.h pow() | | GLOBALE VARIABLES: | % | | ARGUMENTS: | char *pszBase | The string including the digit to be checked | | | PROTOTYPE: | int _CfnTYPE check_modulus10(char *pszBase) ; | | RETURN VALUE: | int 0 = OK | else value - 11 = correct digit | MODULE: | modulus.c |----------------------------------------------------------------------------| | | |----------------------------------------------------------------------------| |1993-09-29/Erik Bachmann \---------------------------------------------------------------------------|*/ int _CfnTYPE check_modulus11(char *pszBase) { char szTmp[11] ; int iTmp = 0 ; /*--------------------*/ strncpy(szTmp, pszBase, strlen(pszBase) - 1) ; szTmp[strlen(pszBase) - 1] = '\0' ; /* Extract base */ iTmp = pszBase[strlen(pszBase) - 1] - '0' ; /* Extract current check digit */ if ( modulus11(szTmp) == iTmp ) return( 0 ) ; /* Check digit is OK */ else return( 11 + modulus11(szTmp) ) ; /* On error return the correct + 11 */ } /*** check_modulus11() ***/ /******************************************************/ #ifdef TEST int main(void) { int iStatus ; /*------------------------------*/ iStatus = modulus11("943457842") ; iStatus = check_modulus11("9434578423") ; iStatus = modulus10("61248") ; iStatus = check_modulus10("612481") ; return( iStatus ) ; } #endif