CODEWITHSUNDEEP
javajavascriptstringhex
UnKnownHer0
UnKnownHer0

Reputation: 63

Hex String to ByteArray

I am trying to figure out how a hexstring to bytearray function in java is generating the correct binary numbers while javascript comes up with something completely different.

Java

public static byte[] hexStringToByteArray(String s) {
    int len = s.length();

    byte[] data = new byte[len / 2];
    for (int i = 0; i < len; i += 2) {
        data[i / 2] = (byte) 
        ((Character.digit(s.charAt(i), 16) << 4) + Character.digit(s.charAt(i+1), 16));


    }
    return data;
}

Javascript

this.hexStringToByteArray = function(s) {

    var len = s.length;
    var data = [];
    for(var i=0; i<(len/2); data[i++]=0) {} 

    for (var i = 0; i < len; i += 2) {

        data[i / 2] = (parseInt(s.charAt(i), 16) << 4)
                             + parseInt(s.charAt(i+1), 16);

    }

    return data;

};

Java:

"a3" = -93;

Javascript:

"a3" = 163;

Without the (byte) cast Java generates the same numbers as javascript does. How can I make javascript generate the same numbers(positive or negative) as Java if you can not specific variables to be bytes?

Upvotes: 4

Views: 973

Answers (1)

morgano
morgano

Reputation: 17422

If what you want is to generate the same result as Java, then you need to make your number be in the range [-128, 127]. Try something like this:

this.hexStringToByteArray = function(s) {

    var len = s.length;
    var data = [];
    for(var i=0; i<(len/2); data[i++]=0) {} 

    for (var i = 0; i < len; i += 2) {

        var value = (parseInt(s.charAt(i), 16) << 4)
                             + parseInt(s.charAt(i+1), 16);

        // "transforms" your integer to the value a Java "byte" would have:
        if(value > 127) {
            value -= 256;
        }

        data[i / 2] = value;

    }

    return data;

};

Upvotes: 3

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