base64 = {}
local __CODE = {
‘A‘, ‘B‘, ‘C‘, ‘D‘, ‘E‘, ‘F‘, ‘G‘, ‘H‘, ‘I‘, ‘J‘, ‘K‘, ‘L‘, ‘M‘, ‘N‘, ‘O‘, ‘P‘,
‘Q‘, ‘R‘, ‘S‘, ‘T‘, ‘U‘, ‘V‘, ‘W‘, ‘X‘, ‘Y‘, ‘Z‘, ‘a‘, ‘b‘, ‘c‘, ‘d‘, ‘e‘, ‘f‘,
‘g‘, ‘h‘, ‘i‘, ‘j‘, ‘k‘, ‘l‘, ‘m‘, ‘n‘, ‘o‘, ‘p‘, ‘q‘, ‘r‘, ‘s‘, ‘t‘, ‘u‘, ‘v‘,
‘w‘, ‘x‘, ‘y‘, ‘z‘, ‘0‘, ‘1‘, ‘2‘, ‘3‘, ‘4‘, ‘5‘, ‘6‘, ‘7‘, ‘8‘, ‘9‘, ‘+‘, ‘/‘,
}
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,
}
--encode
function base64.encode(text)
local len = string.len(text)
local residual = len % 3
len = len - residual
local index = 1
local ret = {}
--处理正好转换的部分
for i =1,len,3 do
local t1 = string.byte(text,i)
local t2 = string.byte(text,i+1)
local t3 = string.byte(text,i+2)
--第一个字符左移16位，第二个8位，第三个0位
local num = t1*65536 + t2*256 + t3
for j = 3,0,-1 do
--右移移18、12、6、0位
local tmp = math.floor(num/(2^(j*6)))
local pos = tmp%64 + 1
ret[index] = __CODE[pos]
index = index + 1
end
end
--处理不能正好转换的部分
if residual == 1 then
local num = string.byte(text,len+1)
--左移4位，总共占8+4=12位，编码位2个base64字符
num = num * 16
--右移6位
local pos = math.floor(num/64)%64 + 1
ret[index] = __CODE[pos]
pos = num%64+1
ret[index+1] = __CODE[pos]
ret[index+2] = ‘=‘
ret[index+3] = ‘=‘
elseif residual ==2 then
local num1 = string.byte(text,len+1)
local num2 = string.byte(text,len+2)
--num1左移10位，num2左移2位
local num = num1*1024 + num2*4
--右移12位
local pos = math.floor(num/4096) % 64 + 1
ret[index] = __CODE[pos]
--右移6位
pos = math.floor(num/64) %64 + 1
ret[index+1] = __CODE[pos]
pos = num%64 + 1
ret[index+2] = __CODE[pos]
ret[index+3] = ‘=‘
end
return table.concat(ret)
end
--decode
function base64.decode(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