bank, a Fortran90 code which can compute the check digit associated with a US Bank Routing Number check digit, or it can report whether a 9-digit code is actually valid.
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bank is available in a C version and a C++ version and a Fortran90 version and a MATLAB version and an Octave version and a Python version.
isbn, a Fortran90 code which can determine the check digit for an International Standard Book Number or report whether a given ISBN is valid.
luhn, a Fortran90 code which computes the Luhn check digit for a string, and can validate a string.
upc, a Fortran90 code which determines the check digit for a Uniform Product Code (UPC) or reports whether a given UPC is valid.