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我想借助 OCR 读取大约 16-20 个字符（AZ，0-9）的序列号。因为每次我想在序列号中添加一个校验字符时，所有字符都不会被正确识别。目前我找到了简单的 Luhn mod N 算法（维基百科）。该算法对于转置错误 (09 => 90) 是不安全的。

来自维基百科的实现：

 char GenerateCheckCharacter(string input) {

    int factor = 2;
    int sum = 0;
    int n = NumberOfValidInputCharacters();

    // Starting from the right and working leftwards is easier since 
    // the initial "factor" will always be "2" 
    **//int index = 0;**
    for (int i = input.Length - 1; i >= 0; i--) {
        int codePoint = CodePointFromCharacter(input[i]);
        int addend = factor * codePoint;

        // Alternate the "factor" that each "codePoint" is multiplied by
        factor = (factor == 2) ? 1 : 2;
        **//factor = index;**


        // Sum the digits of the "addend" as expressed in base "n"
        addend = (addend / n) + (addend % n);
        sum += addend;
        **//index++;**
    }

    // Calculate the number that must be added to the "sum" 
    // to make it divisible by "n"
    int remainder = sum % n;
    int checkCodePoint = (n - remainder) % n;

    return CharacterFromCodePoint(checkCodePoint);
}

NumberOfValidInputCharacters() 将是 36 (AZ, 0-9)

但是，如果我将“因子”变量修改为序列号中字符的实际索引，是否会像以前一样更安全？（参见代码中的 ** ** 行）

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