LUHN
Luhn Check Digit for Error Detection

LUHN is a FORTRAN90 library which demonstrates the calculation and use of the Luhn check digit for error detection.

Licensing:

The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.

Languages:

LUHN is available in a C version and a C++ version and a FORTRAN90 version and a MATLAB version and a Python version.

Related Data and Programs:

ISBN, a FORTRAN90 library which can determine the check digit for an International Standard Book Number or report whether a given ISBN is valid.

UPC, a FORTRAN90 library which can determine the check digit for a Uniform Product Code (UPC) or report whether a given UPC is valid.

Source Code:

• luhn.f90, the source code.

Examples and Tests:

• luhn_test.f90, a sample calling program.
• luhn_test.txt, the output file.

List of Routines:

• CH_IS_DIGIT is TRUE if a character is a decimal digit.
• CH_TO_DIGIT returns the value of a base 10 digit.
• I4VEC_PRINT prints an I4VEC.
• LUHN_CHECK_DIGIT_CALCULATE determines the Luhn check digit of a string.
• LUHN_CHECKSUM determines the Luhn checksum of a string.
• LUHN_IS_VALID determines whether a string with Luhn check digit is valid.
• S_DIGITS_COUNT counts the digits in a string.
• S_TO_DIGITS extracts N digits from a string.
• TIMESTAMP prints the current YMDHMS date as a time stamp.

You can go up one level to the FORTRAN90 source codes.