private static
  java.util.regex.Pattern
      fpPattern() {
    /*
     * We use # instead of * for possessive quantifiers. This lets us strip them out when building
     * the regex for RE2 (which doesn't support them) but leave them in when building it for
     * java.util.regex (where we want them in order to avoid catastrophic backtracking).
     */
    String decimal = "(?:\\d+#(?:\\.\\d*#)?|\\.\\d+#)";