Question

以下是用于在java中对消息进行位填充的方法（public static byte [] bitStuff（byte [] b））。但我无法理解方法中注释掉的行：

 public static byte set_1_at_position(int i, byte b) {
    b |= (128 >> i);
    return b;
}

public static byte set_0_at_position(int i, byte b) {
    b &= (byte) (~(128 >> i));
    return b;
}

public static int get_bit_at_position(int pos, byte b) {
    if ((b & (byte) (128 >> pos)) == 0) {
        return 0;
    }
    return 1;
}



    public static byte[] bitStuff(byte[] b){

            byte[] temp=new byte[b.length*2];
            int size=b.length*8;
            int count_of_one=0;
            int count_of_temp=0;
            for(int i=0;i<size;i++)
            {
                int bit=get_bit_at_position(i%8, b[i/8]); //what is being done here
                if(bit==1)
                {
                    count_of_one++;
                    temp[count_of_temp/8]=set_1_at_position(count_of_temp%8, temp[count_of_temp/8]);  //what is happening in this line
                }
                else
                {
                    count_of_one=0;
                    temp[count_of_temp/8]=set_0_at_position(count_of_temp%8, temp[count_of_temp/8]);
                }

                count_of_temp++;

                if(count_of_one==5)
                {
                    count_of_one=0;
                    //bit stuffing
                    temp[count_of_temp/8]=set_0_at_position(count_of_temp%8, temp[count_of_temp/8]);  // what is happening in this line
                    count_of_temp++;
                }
            }

            byte[] ret=new byte[(count_of_temp+7)/8];
            System.arraycopy(temp, 0, ret, 0, ret.length);

    return ret;

}

任何人都可以解释这些界限吗？

Answer 1

请注意，“size”和“i”变量是计数位（而不是字节）。 get_bit_at_position（i％8，b [i / 8]）; 该行返回“i”位值。 “i”位值等于“i / 8”字节处的“i％8”位值。 set_0_at_position（count_of_temp％8，temp [count_of_temp / 8]）; 这几乎与上述一行相反。它将“i”位设置为零。

理解java中的方法有困难

1 个答案: