Lua实现的Base64编码

ZZBase64 = {}
local string = string

ZZBase64.__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', '+', '/',
};
ZZBase64.__decode = {}
for k,v in pairs(ZZBase64.__code) do
ZZBase64.__decode[string.byte(v,1)] = k - 1
end

function ZZBase64.encode(text)
local len = string.len(text)
local left = len % 3
len = len - left
local res = {}
local index  = 1
for i = 1, len, 3 do
local a = string.byte(text, i )
local b = string.byte(text, i + 1)
local c = string.byte(text, i + 2)
-- num = a<<16 + b<<8 + c
local num = a * 65536 + b * 256 + c
for j = 1, 4 do
--tmp = num >> ((4 -j) * 6)
local tmp = math.floor(num / (2 ^ ((4-j) * 6)))
--curPos = tmp&0x3f
local curPos = tmp % 64 + 1
res[index] = ZZBase64.__code[curPos]
index = index + 1
end
end

if left == 1 then
ZZBase64.__left1(res, index, text, len)
elseif left == 2 then
ZZBase64.__left2(res, index, text, len)
end
return table.concat(res)
end

function ZZBase64.__left2(res, index, text, len)
local num1 = string.byte(text, len + 1)
num1 = num1 * 1024 --lshift 10
local num2 = string.byte(text, len + 2)
num2 = num2 * 4 --lshift 2
local num = num1 + num2

local tmp1 = math.floor(num / 4096) --rShift 12
local curPos = tmp1 % 64 + 1
res[index] = ZZBase64.__code[curPos]

local tmp2 = math.floor(num / 64)
curPos = tmp2 % 64 + 1
res[index + 1] = ZZBase64.__code[curPos]

curPos = num % 64 + 1
res[index + 2] = ZZBase64.__code[curPos]

res[index + 3] = "="
end

function ZZBase64.__left1(res, index,text, len)
local num = string.byte(text, len + 1)
num = num * 16

tmp = math.floor(num / 64)
local curPos = tmp % 64 + 1
res[index ] = ZZBase64.__code[curPos]

curPos = num % 64 + 1
res[index + 1] = ZZBase64.__code[curPos]

res[index + 2] = "="
res[index + 3] = "="
end

function ZZBase64.decode(text)
local len = string.len(text)
local left = 0
if string.sub(text, len - 1) == "==" then
left = 2
len = len - 4
elseif string.sub(text, len) == "=" then
left = 1
len = len - 4
end

local res = {}
local index = 1
local decode = ZZBase64.__decode
for i =1, len, 4 do
local a = decode[string.byte(text,i    )]
local b = decode[string.byte(text,i + 1)]
local c = decode[string.byte(text,i + 2)]
local d = decode[string.byte(text,i + 3)]

--num = a<<18 + b<<12 + c<<6 + d
local num = a * 262144 + b * 4096 + c * 64 + d

local e = string.char(num % 256)
num = math.floor(num / 256)
local f = string.char(num % 256)
num = math.floor(num / 256)
res[index ] = string.char(num % 256)
res[index + 1] = f
res[index + 2] = e
index = index + 3
end

if left == 1 then
ZZBase64.__decodeLeft1(res, index, text, len)
elseif left == 2 then
ZZBase64.__decodeLeft2(res, index, text, len)
end
return table.concat(res)
end

function ZZBase64.__decodeLeft1(res, index, text, len)
local decode = ZZBase64.__decode
local a = decode[string.byte(text, len + 1)]
local b = decode[string.byte(text, len + 2)]
local c = decode[string.byte(text, len + 3)]
local num = a * 4096 + b * 64 + c

local num1 = math.floor(num / 1024) % 256
local num2 = math.floor(num / 4) % 256
res[index] = string.char(num1)
res[index + 1] = string.char(num2)
end

function ZZBase64.__decodeLeft2(res, index, text, len)
local decode = ZZBase64.__decode
local a = decode[string.byte(text, len + 1)]
local b = decode[string.byte(text, len + 2)]
local num = a * 64 + b
num = math.floor(num / 16)
res[index] = string.char(num)
end

function ZZBase64.test()
local data = "a\193\207="
local abc = ZZBase64.encode(data)
print(abc)

def = ZZBase64.decode(abc)
if def == data then
print("yes")
end
end

ZZBase64.test()