char2int & int2char encoding, Lua

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--lua 5.3

local function getsymbols()
    Char2Int = {}
    Int2Char = {}
    local i = 0
    while(i<=string.len(symbols))do
        Char2Int[string.sub(symbols,i,i)] = i
        Int2Char[i]= string.sub(symbols,i,i)
        i = i + 1
    end
    ------------------------------------------------
end

symbols = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
getsymbols()

local function ChangeInt2Char(int)
    local int = tostring(int)
    local maxn = string.len(symbols)
    local str = ""

while(tonumber(int)>maxn)do
        local residue = tostring(math.fmod(tonumber(int),maxn))
        local divizor = tostring((tonumber(int)-tonumber(residue))/maxn)   
        print("( "..int.." - "..residue.." )/ "..maxn.." = "..divizor)
        str = str..Int2Char[tonumber(residue)]
        int = tostring(divizor)
    end
    print("======================================")
    str = str..Int2Char[tonumber(int)]
    return str
end

local function ChangeChar2Int(str)
    str = string.reverse(str)
    local maxn = string.len(symbols)
    local len = string.len(str)
    local int = 0
    local letters = {}
    
    letters[0] = Char2Int[string.sub(str,len,-1)]
    str = string.sub(str,0,string.len(str)-1)
    local i = 1
    while(string.len(str)~=0)do
        letters[i] = Char2Int[string.sub(str,string.len(str),-1)]
        str = string.sub(str,0,string.len(str)-1)
        i = i + 1
    end
    
    local a = 1
    while(a<i)do
        local n = tostring(maxn^a)
        int = tostring(tonumber(int)+letters[a]*tonumber(n))
        a = a + 1
    end
    int = int + letters[0]
    return tostring(int)
end

print("Int2Char: "..ChangeInt2Char(10^13+5))
print("Char2Int: "..ChangeChar2Int("INSJq2P1"))
--precision cap is ~10^14 ???

[ + ] Show input
Absolute running time: 0.06 sec, cpu time: 0.02 sec, memory peak: 3 Mb, absolute service time: 0,08 sec