package computernetwork;

// 循環(huán)冗余檢驗(yàn) Cyclic Redundancy Check (CRC)
public class CRC {

    private int[] generatingCode; // 生成碼

    // 設(shè)置生成碼
    public void setGeneratingCode(String str) {
        generatingCode = stringToArray(str);
    }

    // 獲取幀檢驗(yàn)序列
    public String getFCS(String message) {
        for (int i = 0; i < generatingCode.length - 1; i++) {
            message += "0";
        }
        return getRemainder(stringToArray(message));
    }

    // 判斷接受碼是否產(chǎn)生跳變
    public boolean judge(String res) {
        return Integer.parseInt(getRemainder(stringToArray(res))) == 0;
    }

    // 將01字符串轉(zhuǎn)換為數(shù)組
    private int[] stringToArray(String str) {
        char[] chars = str.toCharArray();
        int[] res = new int[chars.length];
        for (int i = 0; i < chars.length; i++) {
            res[i] = chars[i] - '0';
        }
        return res;
    }

    // 求余數(shù)
    private String getRemainder(int[] code) {
        int len = code.length - generatingCode.length + 1;
        for (int i = 0; i < len; i++) {
            if (code[i] != 0) {
                for (int j = 0; j < generatingCode.length; j++) {
                    code[i + j] ^= generatingCode[j];
                }
            }
        }
        StringBuilder res = new StringBuilder();
        for (int i = len; i < code.length; i++) {
            res.append(code[i]);
        }
        return res.toString();
    }
}

class TestCRC {
    public static void main(String[] args) {
        CRC crc = new CRC();
        crc.setGeneratingCode("10011");
        System.out.println(crc.getFCS("1101011011")); // 1110
        System.out.println(crc.judge("11010110111110")); // true
        System.out.println(crc.judge("11010110111011")); // false
    }
}