lint_csumalpha.c File Reference

Purpose

The csumalpha linter ensures that the data has a valid alphanumeric check character pair.

Remarks

The process for validating the GS1 alphanumeric check character pair is described in the GS1 General Specifications section "Check character calculation (for alphanumeric keys)".

Functional Description

gs1_lint_csumalpha()

GS1_SYNTAX_DICTIONARY_API gs1_lint_err_t gs1_lint_csumalpha	(	const char *const	data,
		size_t *const	err_pos,
		size_t *const	err_len
	)

Used to ensure that the AI component has a valid alphanumeric check character pair.

Parameters

[in]	data	Pointer to the null-terminated data to be linted. Must not be NULL.
[out]	err_pos	To facilitate error highlighting, the start position of the bad data is written to this pointer, if not NULL.
[out]	err_len	The length of the bad data is written to this pointer, if not NULL.

Returns

GS1_LINTER_OK if okay.

GS1_LINTER_INCORRECT_CHECK_PAIR if the data contains an incorrect check character pair.

GS1_LINTER_TOO_SHORT_FOR_CHECK_PAIR if the data is too short.

GS1_LINTER_TOO_LONG_FOR_CHECK_PAIR_IMPLEMENTATION if the data is too long for this implementation of the check character pair algorithm. GS1_LINTER_INVALID_CSET82_CHARACTER if any of the data characters are not in CSET 82.

Note

The return value GS1_LINTER_TOO_LONG_FOR_CHECK_PAIR_IMPLEMENTATION represents exceeding an implementation-specific limit. Some implmenetations may choose to support longer data inputs.

{
 
        /*
         *  Set of prime weights used to derive alpha check characters.
         *
         *  Here we have the first 97 since that is the maximum length of any
         *  AI is currently 99. Implementations may choose to support longer
         *  data inputs.
         *
         */
        static const unsigned int primes[] = {
                  2,   3,   5,   7,  11,  13,  17,  19,  23,  29,  31,  37,
                 41,  43,  47,  53,  59,  61,  67,  71,  73,  79,  83,  89,
                 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151,
                157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223,
                227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281,
                283, 293, 307, 311, 313, 317, 331, 337, 347, 349, 353, 359,
                367, 373, 379, 383, 389, 397, 401, 409, 419, 421, 431, 433,
                439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 503,
                509
        };
 
        /*
         * Sequence of all characters in CSET 32, ordered by weight.
         */
        static const char* const cset32 = "23456789ABCDEFGHJKLMNPQRSTUVWXYZ";
 
        /*
         * CSET82 character weights lookup table (0 = invalid; weight off by 1)
         */
        static const unsigned char cset82_weights[256] = {
                ['!'] = 1, ['"'] = 2, ['%'] = 3, ['&'] = 4, ['\''] = 5, ['('] = 6,
                [')'] = 7, ['*'] = 8, ['+'] = 9, [','] = 10, ['-'] = 11, ['.'] = 12,
                ['/'] = 13, ['0'] = 14, ['1'] = 15, ['2'] = 16, ['3'] = 17, ['4'] = 18,
                ['5'] = 19, ['6'] = 20, ['7'] = 21, ['8'] = 22, ['9'] = 23, [':'] = 24,
                [';'] = 25, ['<'] = 26, ['='] = 27, ['>'] = 28, ['?'] = 29, ['A'] = 30,
                ['B'] = 31, ['C'] = 32, ['D'] = 33, ['E'] = 34, ['F'] = 35, ['G'] = 36,
                ['H'] = 37, ['I'] = 38, ['J'] = 39, ['K'] = 40, ['L'] = 41, ['M'] = 42,
                ['N'] = 43, ['O'] = 44, ['P'] = 45, ['Q'] = 46, ['R'] = 47, ['S'] = 48,
                ['T'] = 49, ['U'] = 50, ['V'] = 51, ['W'] = 52, ['X'] = 53, ['Y'] = 54,
                ['Z'] = 55, ['_'] = 56, ['a'] = 57, ['b'] = 58, ['c'] = 59, ['d'] = 60,
                ['e'] = 61, ['f'] = 62, ['g'] = 63, ['h'] = 64, ['i'] = 65, ['j'] = 66,
                ['k'] = 67, ['l'] = 68, ['m'] = 69, ['n'] = 70, ['o'] = 71, ['p'] = 72,
                ['q'] = 73, ['r'] = 74, ['s'] = 75, ['t'] = 76, ['u'] = 77, ['v'] = 78,
                ['w'] = 79, ['x'] = 80, ['y'] = 81, ['z'] = 82
        };
 
        size_t pos, len;
        uint32_t sum = 0;       /* Sufficient for 97-prime implementation */
 
        assert(data);
 
        /*
         * Find length constraining data to the number of primes that we have.
         *
         */
        for (len = 0; data[len] != '\0'; len++) {
                if (GS1_LINTER_UNLIKELY(len >= sizeof(primes) / sizeof(primes[0]) + 2))
                        GS1_LINTER_RETURN_ERROR(
                                GS1_LINTER_TOO_LONG_FOR_CHECK_PAIR_IMPLEMENTATION,
                                0,
                                len + 1
                        );
        }
 
        /*
         * Data must include at least the check character pair.
         *
         */
        if (GS1_LINTER_UNLIKELY(len < 2))
                GS1_LINTER_RETURN_ERROR(
                        GS1_LINTER_TOO_SHORT_FOR_CHECK_PAIR,
                        0,
                        len
                );
 
        /*
         * Handling the two-character case now avoids conditionals later.
         *
         */
        if (len == 2) {
                if (GS1_LINTER_UNLIKELY(data[0] != '2' || data[1] != '2'))
                        GS1_LINTER_RETURN_ERROR(
                                GS1_LINTER_INCORRECT_CHECK_PAIR,
                                len - 2,
                                2
                        );
                GS1_LINTER_RETURN_OK;
        }
 
        /*
         * Sum of data-character values weighted by increasing prime values,
         * from right to left, modulo 1021.
         *
         * The check characters are valid when their values match the above
         * data checksum with its 10-bit value split evenly into two 5-bit
         * values.
         *
         * The data character values are defined by their respective positions
         * in CSET 82.
         *
         * The check character pair values are defined by their respective
         * positions in CSET 32.
         *
         */
        for (pos = 0; pos < len - 2; pos++) {
                if (GS1_LINTER_UNLIKELY(cset82_weights[(unsigned char)data[pos]] == 0))
                        GS1_LINTER_RETURN_ERROR(
                                GS1_LINTER_INVALID_CSET82_CHARACTER,
                                pos,
                                1
                        );
                sum += (unsigned int)(cset82_weights[(unsigned char)data[pos]] - 1) * primes[len - 3 - pos];
        }
        sum %= 1021;    /* Overflow not possible with uint32_t */
 
        if (GS1_LINTER_UNLIKELY(data[len-2] != cset32[sum >> 5] || data[len-1] != cset32[sum & 31]))
                GS1_LINTER_RETURN_ERROR(
                        GS1_LINTER_INCORRECT_CHECK_PAIR,
                        len - 2,
                        2
                );
 
        GS1_LINTER_RETURN_OK;
 
}