little byte lib

local byte = {}
function byte.split(str, a, b)
    local insert = table.insert
    if type(a) == 'table' then
        local t = {}
        local cursor = 0
        for i = 1, #a do
            insert(t, str:sub(cursor+1, cursor+a[i]))
            cursor = cursor + #(t[#t])
        end
        return b and unpack(t) or t
    end
    a, b = a or 0, b or 1
    return str:sub(a+1, a+b)
end

local max_int = 2^8
function byte.encode(num, len)
    local insert, char = table.insert, string.char
    if len and num > max_int^len - 1 then
        error('Encode too big number: %d, max is %d', num, max^len)
    end
    local t={}
    while num > 0 do
        local rest = num % 255
        insert(t, char(rest))
        num = (num - rest) / 255
    end
    if len and #t < len then insert(t, ('\0'):rep(len - #t)) end
    return table.concat(t)
end

function byte.decode(c)
    local insert = table.insert
    local n = 0
    c = c:reverse()
    for j = 1, #c do
        n = n + c:sub(j, j):byte()*255^(#c-j)
    end
    return n
end

return byte