/*
 * This module implements a function for computing the Luhn check digit
 * for ICCIDs that follow the 18+1 convention.
 */

#include <sys/types.h>

compute_iccid_luhn(digits)
	u_char *digits;
{
	int i, dig, sum;

	sum = 0;
	for (i = 0; i < 18; i++) {
		dig = digits[i];
		if (i & 1) {
			dig *= 2;
			if (dig > 9)
				dig -= 9;
		}
		sum += dig;
	}
	dig = sum % 10;
	if (dig)
		dig = 10 - dig;
	return dig;
}