Base64编码的实现

关于javascript中的base64编码的解决办法。主要是编码的源代码。文章于2007年35月28日发布在http://www.12px.net

Base64内容传送编码被设计用来把任意序列的8位字节描述为一种不易被人直接识别的形式(The Base64 Content-Transfer-Encoding is designed to represent arbitrary sequences of octets in a form that need not be humanly readable.)。好玩，弄来不被人识别？不识别就不识别嘛，反正程序能之别就行了。

这个编码为什么叫Base64呢？这是应为它的转换需要依赖一张64个字符的转换表，叫做The Base64 Alphabet。 Base64以3个字节为一个转换单位，把这24bits分为4份，高位补零，再查前面说的那个转换表，就编码完毕了。如果被转换的数据(以byte为单位)不能被3整除，按余数补"="(pad)，当然最多也就只有两种可能，不是补一个pad就是补两个pad。

<script language="javascript"> 
var Base64Alphabet = ['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', '+', '/'];

function EncodeBase64(string) 
{ 
var hexString = string.getGBCode(); 
window.status = hexString; 
var base64 = ''; 
var B64A = Base64Alphabet; 
var padCount = hexString.length%3; 
var count = parseInt(hexString.length/6); 
var i = 0; 
for ( i=0 ; i < count ; ++i ) 
{ 
var intA = parseInt(hexString.charAt(i*6+0)+hexString.charAt(i*6+1), 16); 
var intB = parseInt(hexString.charAt(i*6+2)+hexString.charAt(i*6+3), 16); 
var intC = parseInt(hexString.charAt(i*6+4)+hexString.charAt(i*6+5), 16); 
var part1 = intA >> 2; 
var part2 = ((intA & 0x03) << 4) | (intB >> 4); 
var part3 = ((intB & 0x0f) << 2) | (intC >> 6); 
var part4 = intC & 0x3f; 
base64 += B64A[part1] + B64A[part2] + B64A[part3] + B64A[part4]; 
} 
if ( padCount == 1 ) 
{ 
var intA = parseInt(hexString.charAt(i*6+0)+hexString.charAt(i*6+1), 16); 
var intB = parseInt(hexString.charAt(i*6+2)+hexString.charAt(i*6+3), 16); 
var part1 = intA >> 2; 
var part2 = ((intA & 0x03) << 4) | (intB >> 4); 
var part3 = ((intB & 0x0f) << 2); 
base64 += B64A[part1] + B64A[part2] + B64A[part3] + '='; 
} 
if ( padCount == 2 ) 
{ 
var intA = parseInt(hexString.charAt(i*6+0)+hexString.charAt(i*6+1), 16); 
var part1 = intA >> 2; 
var part2 = ((intA & 0x03) << 4); 
base64 += B64A[part1] + B64A[part2] + '=='; 
} 
return base64; 
} 
</script><script language="vbscript"> 
function vbGetGBCode(str) 
dim i, length, s 
length = len(str) 
for i=1 to length 
hexCode = hex(asc(str.charAt(i-1))) 
if (len(hexCode) mod 2) = 0 then 
s = s & hexCode 
else 
s = s & "0" & hexCode 
end if 
next 
vbGetGBCode = s 
end function 
</script><script language="javascript"> 
String.prototype.getGBCode = function() 
{ 
return vbGetGBCode(this); 
} 
</script><script language="javascript"> 
var Base64Alphabet = ['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', '+', '/'];

function EncodeBase64(string) 
{ 
var hexString = string.getGBCode(); 
window.status = hexString; 
var base64 = ''; 
var B64A = Base64Alphabet; 
var padCount = hexString.length%3; 
var count = parseInt(hexString.length/6); 
var i = 0; 
for ( i=0 ; i < count ; ++i ) 
{ 
var intA = parseInt(hexString.charAt(i*6+0)+hexString.charAt(i*6+1), 16); 
var intB = parseInt(hexString.charAt(i*6+2)+hexString.charAt(i*6+3), 16); 
var intC = parseInt(hexString.charAt(i*6+4)+hexString.charAt(i*6+5), 16); 
var part1 = intA >> 2; 
var part2 = ((intA & 0x03) << 4) | (intB >> 4); 
var part3 = ((intB & 0x0f) << 2) | (intC >> 6); 
var part4 = intC & 0x3f; 
base64 += B64A[part1] + B64A[part2] + B64A[part3] + B64A[part4]; 
} 
if ( padCount == 1 ) 
{ 
var intA = parseInt(hexString.charAt(i*6+0)+hexString.charAt(i*6+1), 16); 
var intB = parseInt(hexString.charAt(i*6+2)+hexString.charAt(i*6+3), 16); 
var part1 = intA >> 2; 
var part2 = ((intA & 0x03) << 4) | (intB >> 4); 
var part3 = ((intB & 0x0f) << 2); 
base64 += B64A[part1] + B64A[part2] + B64A[part3] + '='; 
} 
if ( padCount == 2 ) 
{ 
var intA = parseInt(hexString.charAt(i*6+0)+hexString.charAt(i*6+1), 16); 
var part1 = intA >> 2; 
var part2 = ((intA & 0x03) << 4); 
base64 += B64A[part1] + B64A[part2] + '=='; 
} 
return base64; 
} 
</script><script language="vbscript"> 
function vbGetGBCode(str) 
dim i, length, s 
length = len(str) 
for i=1 to length 
hexCode = hex(asc(str.charAt(i-1))) 
if (len(hexCode) mod 2) = 0 then 
s = s & hexCode 
else 
s = s & "0" & hexCode 
end if 
next 
vbGetGBCode = s 
end function 
</script><script language="javascript"> 
String.prototype.getGBCode = function() 
{ 
return vbGetGBCode(this); 
} 
</script>

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