Question

I read byte[] from socket as Param_Code. there is a condition for Param_Code as below:

• Option 1: Sometimes the Param_Code corresponds to the ID

• Option 2: Sometimes the Param_Code corresponds to 0x40000000 + the ID

• Option 3: Sometimes the Param_Code corresponds to 0x80000000 + the ID

This is my code:

byte[] cbuf = new byte[4];

socketReader.read(cbuf, 0, 4);

int Param_Code = byteArrayToIntBI(cbuf, 0);

public static int byteArrayToIntBI(byte[] b, int offset) {
    int value = 0;
    for (int i = 3; i > -1; i--) {
        int shift = (i) * 8;
        value += (b[i + offset] & 0x000000FF) << shift;
    }
    return value;
}

My question is, How can i know (with if statement or something else) when the Param_Code is one of above option?

How can i get ID?

if( ? ){
        it is Option 1 and ID = ?
}else if( ? ){
        it is Option 1 and ID = ?
}else if( ? ){
        it is Option 1 and ID = ?
}

Answer 1

You should add some restriction on ID. Because we cannot apply mask in that case.

Imagine, that you got 0x81234123. It can be:

• ID 0x81234123
• ID 0x41234123
• ID 0x01234123

Provide additional condition to avoid that ambiguity.
i can only assume that your ID doesn’t include first hexadecimal number so, in that case use mask: ID = NUM & 0x0FFFFFFF

NUM is actually your byte[4]