src/main/java/com/groupon/uuid/UUID.java
private static byte mapToByte(char a, char b) {
        int ai = intValue(a);
        int bi = intValue(b);
        return (byte) ((ai << 4) | bi);
    }
private static byte mapToByte(char a, char b) {
        int ai = intValue(a);
        int bi = intValue(b);
        return (byte) ((ai << 4) | bi);
    }
Map two hex characters to 4-bit numbers and combine them to produce 8-bit number in byte.
@param a First hex character.
@param b Second hex character.
@return Byte representation of given hex characters.