Tengo una función escrita en C #, quiero convertirla en objetivo-c. ¿Cómo hacerlo?

public static string UnicodeUnSign(string s)
{
    const string uniChars = "àáảãạâầấẩẫậăằắẳẵặèéẻẽẹêềếểễệđìíỉĩịòóỏõọôồốổỗộơờớởỡợùúủũụưừứửữựỳýỷỹỵÀÁẢÃẠÂẦẤẨẪẬĂẰẮẲẴẶÈÉẺẼẸÊỀẾỂỄỆĐÌÍỈĨỊÒÓỎÕỌÔỒỐỔỖỘƠỜỚỞỠỢÙÚỦŨỤƯỪỨỬỮỰỲÝỶỸỴÂĂĐÔƠƯ";
    const string koDauChars = "aaaaaaaaaaaaaaaaaeeeeeeeeeeediiiiiooooooooooooooooouuuuuuuuuuuyyyyyAAAAAAAAAAAAAAAAAEEEEEEEEEEEDIIIOOOOOOOOOOOOOOOOOOOUUUUUUUUUUUYYYYYAADOOU";

    if (string.IsNullOrEmpty(s))
    {
        return s;
    }

    string retVal = String.Empty;
    for (int i = 0; i < s.Length; i++)
    {
        int pos = uniChars.IndexOf(s[i].ToString());
        if (pos >= 0)
            retVal += koDauChars[pos];
        else
            retVal += s[i];
    }
    return retVal;
}