java求校验和的算法

 

public class Test1 {

    /**
     * 求校验和的算法
     * @param b 需要求校验和的字节数组
     * @return 校验和
     */
    private byte sumCheck(byte[] b, int len){
        int sum = 0;
        for(int i = 0; i < len; i++){
            sum = sum + b[i];
        }
        if(sum > 0xff){ //超过了255,使用补码(补码 = 原码取反 + 1)
            sum = ~sum;
            sum = sum + 1;
        }
        return (byte) (sum & 0xff);
    }

    @Test
    public void test1(){
        byte[] b = new byte[7];
        b[0] = (byte) 0xfd;
        b[1] = (byte) 0xfc;
        b[2] = (byte) 0x08;
        b[3] = (byte) 0x80;
        b[4] = (byte) 0x02;
        b[5] = (byte) 0x00;
        b[6] = (byte) 0x0a;
        byte result = sumCheck(b, 7);
        System.out.printf("%x", result);//正确的结果应该是8d
    }
}

 

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