local __ASCII_CODE = {
[65]=0,[66]=1,[67]=2,[68]=3,[69]=4,[70]=5,[71]=6,[72]=7,[73]=8,[74]=9,[75]=10,
[76]=11,[77]=12,[78]=13,[79]=14,[80]=15,[81]=16,[82]=17,[83]=18,[84]=19,[85]=20,[86]=21,
[87]=22,[88]=23,[89]=24,[90]=25,[97]=26,[98]=27,[99]=28,[100]=29,[101]=30,[102]=31,[103]=32,
[104]=33,[105]=34,[106]=35,[107]=36,[108]=37,[109]=38,[110]=39,[111]=40,[112]=41,[113]=42,[114]=43,
[115]=44,[116]=45,[117]=46,[118]=47,[119]=48,[120]=49,[121]=50,[122]=51,[48]=52,[49]=53,[50]=54,
[51]=55,[52]=56,[53]=57,[54]=58,[55]=59,[56]=60,[57]=61,[43]=62,[47]=63,
}

function base64decode(text)

local len = string.len(text)
if(len%4 ~= 0) then
    return nil
end
local residual = 0
if string.sub(text,len-1) == '==' then
    residual = 2
    len = len - 4
elseif string.sub(text,len) == '=' then
    residual = 1
    len = len - 4
end
local index = 1
local ret = {}

--处理正好转换的部分

for i = 1,len,4 do
    local t1 = __ASCII_CODE[string.byte(text,i)]
    local t2 = __ASCII_CODE[string.byte(text,i+1)]
    local t3 = __ASCII_CODE[string.byte(text,i+2)]
    local t4 = __ASCII_CODE[string.byte(text,i+3)]
    local num = t1*262144 + t2*4096 + t3*64 + t4
    local t5 = string.char(num%256)
    num = math.floor(num/256)
    local t6 = string.char(num%256)
    num = math.floor(num/256)
    local t7 = string.char(num%256)
    ret[index] = t7
    ret[index+1] = t6
    ret[index+2] = t5
    index = index+3
end

--处理不能正好转换的部分

if residual == 1 then
    local t8 = __ASCII_CODE[string.byte(text,len+1)]
    local t9 = __ASCII_CODE[string.byte(text,len+2)]
    local t10 = __ASCII_CODE[string.byte(text,len+3)]
    local num = t8*4096 + t9*64 + t10
    local pos = math.floor(num/1024) % 256
    ret[index] = string.char(pos)
    pos = math.floor(num/4) % 256
    ret[index+1] = string.char(pos)
elseif residual ==2 then
    local t8 = __ASCII_CODE[string.byte(text,len+1)]
    local t9 = __ASCII_CODE[string.byte(text,len+2)]
    local num = t8*64 + t9
    local pos = math.floor(num/16)
    ret[index] = string.char(pos)
end
return table.concat(ret)

end
--自己写的不行这个

我也想知道