do

local function splittail(tsrc, tsubstr, tlist)
    local t_strat = 0;
    local t_end = 0;
    local tail = '';
    local first = '';
    t_start, t_end = string.find(tsrc, tsubstr);
    first = string.sub(tsrc, 0, t_start - 1);
    tail = string.sub(tsrc, t_end + 1);
    table.insert(tlist, first);
    t_start = nil;
    t_end = nil;
    t_start, t_end = string.find(tail, tsubstr);
    if t_start ~= nil then
        splittail(tail, tsubstr, tlist);
    else
        table.insert(tlist, tail);
        return tlist;
    end
end

local function split(str, substr)
    local pos_start = nil;
    local pos_end = nil;
    local list = {};
    local tail = '';
    pos_start, pos_end = string.find(str, substr);
    if pos_start == nil then
        return nil;
    else
        first = string.sub(str, 0, pos_start - 1);
        table.insert(list, first);
        tail = string.sub(str, tonumber(pos_end) + 1);
        pos_start = nil;
        pos_end = nil;
        pos_start, pos_end = string.find(tail, substr);
        if pos_start == nil then
            table.insert(list, tail);
            return list;
        else
            splittail(tail, substr, list);
            return list;
        end
    end
end

local function m8bin(x)
    result = '';
    while x > 0
    do
        mod = x % 2;
        x, y = math.modf(x / 2);
        result = tostring(mod) .. result;
    end

    prepos = (8 - string.len(result));
    while prepos > 0
    do
        result = '0' .. result;
        prepos = prepos - 1;
    end
    return result;
end

local function ip2bin(ip)
    slist = split(ip, '%.');
    if slist ~= nil then
        ip1 = m8bin(tonumber(slist[1]));
        ip2 = m8bin(tonumber(slist[2]));
        ip3 = m8bin(tonumber(slist[3]));
        ip4 = m8bin(tonumber(slist[4]));
        res = ip1 .. ip2 .. ip3 .. ip4;
        return res;
    else
        return nil;
    end
end

tool = {
    splittail = splittail,
    split = split,
    m8bin = m8bin,
    ip2bin = ip2bin,
}

end