The long and integer normalizers don't handle negative numbers correctly. about mango

[eawagner]

I think I found a clean way to implement this for now. I am waiting a little while to put this in to apply it after the Types API changes as it will simplify the implementation.

Edit: removed the unnecessary character by simply flipping the first bit. This logic was borrowed from Keith Turners Lexicoders. I however simply use Long.MIN_VALUE (0x8000000000000000L).

/**
* Helper function simply because Long.parseLong(hex,16) does not handle negative numbers that were 
* converted to hex.
*/
private static long fromHex(String hex) {
    long value = 0;
    for (int i = 0; i < hex.length(); i++)
        value = (value << 4) | digit(hex.charAt(i), 16);

    return value;
}

public String normalize(Long value) {
    //First I flip the first bit (not the same as multiplying by -1) 
    //The second part works because java represents negative numbers as 2's compliment
    //Then when it converts to hex in the format, it simply encodes the bits ignoring sign.
    //This property means that negative numbers when converted to hex are already lexicographically sorted.
    return String.format("%016x", value ^ Long.MIN_VALUE);
}

public Long denormalize(String value) {
    //flip first bit back
    return fromHex(value) ^ Long.MIN_VALUE;
}