src/main/java/com/groupon/uuid/UUID.java
private static int intValue(char x) {
        if (x >= '0' && x <= '9')
            return x - '0';
        if (x >= 'a' && x <= 'f')
            return x - 'a' + 10;
        if (x >= 'A' && x <= 'F')
            return x - 'A' + 10;
        throw new RuntimeException("Error parsing UUID at character: " + x);
    }
private static int intValue(char x) {
        if (x >= '0' && x <= '9')
            return x - '0';
        if (x >= 'a' && x <= 'f')
            return x - 'a' + 10;
        if (x >= 'A' && x <= 'F')
            return x - 'A' + 10;
        throw new RuntimeException("Error parsing UUID at character: " + x);
    }
This method maps a hex character to its 4-bit representation in an int.
@param x Hex character in the range ('0' - '9', 'a' - 'f', 'A' - 'F').
@return 4-bit number in int representing hex offset from 0.