}
        }
        return sb.toString();
    }

    private static char hankakuKatakanaToZenkakuKatakana(final char c) {
        if (c >= HANKAKU_KATAKANA_FIRST_CHAR && c <= HANKAKU_KATAKANA_LAST_CHAR) {
            return ZENKAKU_KATAKANA[c - HANKAKU_KATAKANA_FIRST_CHAR];
        }
        return c;
    }

    /**
     * Merges two characters, handling voiced and semi-voiced sound marks.