lua base64

local b='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
local sgsub, sbyte, ssub, schar, sfind = string.gsub, string.byte, string.sub, string.char, string.find

-- encoding
function enc(data)
    return ((sgsub(data, '.', function(x)
        local r,b='',sbyte(x)
        for i=8,1,-1 do r=r..(b%2^i-b%2^(i-1)>0 and '1' or '0') end
        return r;
    end)..'0000'):gsub('%d%d%d?%d?%d?%d?', function(x)
        if (#x < 6) then return '' end
        local c=0
        for i=1,6 do c=c+(ssub(x,i,i)=='1' and 2^(6-i) or 0) end
        return ssub(b, c+1,c+1)
    end)..({ '', '==', '=' })[#data%3+1])
end

-- decoding
function dec(data)
    data = sgsub(data, '[^'..b..'=]', '')
    return (sgsub(data, '.', function(x)
        if (x == '=') then return '' end
        local r,f='',(sfind(b, x)-1)
        for i=6,1,-1 do r=r..(f%2^i-f%2^(i-1)>0 and '1' or '0') end
        return r;
    end):gsub('%d%d%d?%d?%d?%d?%d?%d?', function(x)
        if (#x ~= 8) then return '' end
        local c=0
        for i=1,8 do c=c+(ssub(x,i,i)=='1' and 2^(8-i) or 0) end
        return schar(c)
    end))
end