presto-parser/src/main/java/io/prestosql/sql/parser/AstBuilder.java/AstBuilder/isHexDigit
class AstBuilder:    private static boolean isHexDigit(char c)
    {
        return ((c >= '0') && (c <= '9')) ||
                ((c >= 'A') && (c <= 'F')) ||
                ((c >= 'a') && (c <= 'f'));
    }