Base24、Base64编码的几种程序实现
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可能很多人听说过
Base64
编码，很少有人听说过Base24编码，Base24编码主要应用在序列号生成上，其实基本的算法思想都是一样的，只是编码的模式有点变化。
Base64
所对应的编码表是
ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=
共计64位。
而Base24所对应的编码表是
BCDFGHJKMPQRTVWXY2346789
共计24位，这里主要去掉了一些对于序列号来说不容易识别和容易混淆的字符。
具体算法网上都有介绍我就不再赘述，下面直接谈怎么编码实现吧:-)
对于 Base64 算法的C语言实现，大家可以参考Bob Trower的经典开源项目b64.c，网址是 http://base64.sourceforge.net/ 。
在这里我要谈的是如何用ASP进行 Base64 编码，网上搜索出的一大堆算法不是太复杂就是运行不准确，其实ASP的Base64编码可以很简单，当然要用到服务器的一个COM组件XmlDom，具体思路是这样的，首先创建个临时的节点tmp，然后给结点tmp，设置datatype = "bin.base64"，这样就可以进行相应的编解码了，对于文本字符串的编解码还要用ADODB.Stream进行一次编码转换。
Base64的ASP实现：
Class CBase64
Private objXmlDom
Private objXmlNode
' GetObjectParam() 这个函数实现参考了开源项目PJBlog
Private Function GetObjectParam()
On Error Resume Next
Dim Temp
GetObjectParam = "Microsoft.XMLDOM"
Err = 0
Dim TmpObj
Set TmpObj = Server.CreateObject(GetObjectParam)
Temp = Err.Number
If Temp = 1 Or Temp = -2147221005 Then
GetObjectParam = "Msxml2.DOMDocument.5.0"
End If
Err.Clear
Set TmpObj = Nothing
Err = 0
End Function
Private Sub Class_Initialize()
Set objXmlDom = Server.CreateObject(GetObjectParam())
End Sub
Private Sub Class_Terminate()
Set objXmlDom = Nothing
End Sub
Public Function encode(AnsiCode)
encode = ""
Set objXmlNode = objXmlDom.createElement("tmp")
objXmlNode.datatype = "bin.base64"
objXmlNode.nodeTypedvalue = AnsiCode
encode = objXmlNode.Text
Set objXmlNode = Nothing
End Function
Public Function decode(base64Code)
On Error Resume Next
decode = ""
Set objXmlNode = objXmlDom.createElement("tmp")
objXmlNode.datatype = "bin.base64"
objXmlNode.Text = base64Code
decode = objXmlNode.nodeTypedvalue
Set objXmlNode = Nothing
If Err Then
Err.Clear
End If
End Function
' 以下函数编码字符串
Public Function encodeText(ByVal str)
On Error Resume Next
Dim ado, r: r = ""
If str <> "" Then
Set ado = Server.CreateObject("ADODB.Stream")
With ado
.Charset = "gb2312"
.Type = 2
If .State = 0 Then .Open
.WriteText str
.Position = 0
.Type = 1
r = encode(.Read(-1))
.Close
End With
Set ado = Nothing
End If
If Err Then Err.Clear: r = ""
encodeText = r
End Function
' 以下函数解码字符串
Public Function decodeText(ByVal str)
On Error Resume Next
Dim ado, r: r = ""
If str <> "" Then
Set ado = Server.CreateObject("ADODB.Stream")
With ado
.Charset = "gb2312"
.Type = 1
If .State = 0 Then .Open
.Write (decode(str))
.Position = 0
.Type = 2
r = .ReadText(-1)
.Close
End With
Set ado = Nothing
End If
If Err Then Err.Clear: r = ""
decodeText = r
End Function
End Class写到这里想起以前项目里改写过一段Base64和16进制互转的代码，在这里与大家分享下。
' Base64转16进制
Function B64ToHex(ByVal strContent)
Dim i,strReturned, b64pad, _
b64map, chTemp, intLocate, k , slop
strReturned = "" : k = 0
b64map="ABCDEFGHIJKLMNOPQRSTUVWXYZ" &_
"abcdefghijklmnopqrstuvwxyz0123456789+/"
b64pad="="
For i=0 To Len(strContent)-1
chTemp = Mid(strContent, i+1, 1)
If chTemp = b64pad Then Exit For
intLocate = InStr(1, b64map, chTemp, 0)-1
If intLocate > -1 Then
Select Case K
Case 0
strReturned = strReturned &_
Int2Char(Int(intLocate / 4))
slop = intLocate And 3 : k = 1
Case 1
strReturned = strReturned &_
Int2Char( (slop * 4) Or (Int(intLocate / 16)) )
slop = intLocate And &h0f : k = 2
Case 2
strReturned = strReturned &_
Int2Char(slop) & Int2Char(Int(intLocate / 4))
slop = intLocate And 3 : k=3
Case Else
strReturned = strReturned &_
Int2Char( (slop * 4) Or (Int(intLocate / 16)) ) &_
Int2Char(intLocate And &h0f)
k = 0
End Select
End If
Next
If k=1 Then strReturned = strReturned & Int2Char(slop * 4)
B64ToHex = strReturned
End Function
' 16进制转Base64
Function HexToB64(ByVal strContent)
Dim i, c, strReturned, b64map, b64pad, intLen
b64map="ABCDEFGHIJKLMNOPQRSTUVWXYZ" &_
"abcdefghijklmnopqrstuvwxyz0123456789+/"
b64pad="="
intLen = Len(strContent)
For i=0 To intLen-3 Step 3
c=Clng("&h" & Mid(strContent,i+1,3))
strReturned = strReturned &_
Mid(b64map, Int(c / 64 +1), 1) &_
Mid(b64map, (c And 63)+1, 1)
Next
If i+1=intLen Then
c =Clng("&h" & Mid(strContent,i+1,1))
strReturned = strReturned & Mid(b64map, c * 4 + 1, 1)
ElseIf i+2=intLen Then
c =Clng("&h" & Mid(strContent,i+1,2))
strReturned = strReturned & Mid(b64map, Int(c / 4) + 1, 1) &_
Mid(b64map, (c And 3)*16+1, 1)
End If
While (Len(strReturned) And 3) >0
strReturned = strReturned & b64pad
Wend
HexToB64 = strReturned
End Function有关Base24的代码实现网上也有很多，这里给出两种不同程序语言的实现供参考。
Base24的C语言实现
static const char sel[] = {
'B','C','D','F','G',
'H','J','K','M','P',
'Q','R','T','V','W',
'X','Y','2','3','4',
'6','7','8','9', '\0'};
char *b24e(char *buf, unsigned char *byst, size_t sizeOfBytes)
{
int i = 0;
unsigned char *p = byst;
while ((size_t)(i = (p-byst)) < sizeOfBytes) {
buf[2*i] = sel[((*p) >> 4)];
buf[(2*i)+1] = sel[23 - ((*p) & 0x0f)];
p++;
}
buf[(2*i)+1] = '\0';
return buf;
}
unsigned char *b24d(unsigned char *buf, char *str, size_t countOfChars)
{
size_t i;
char *p = str;
char *loc[2];
unsigned char n[2];
if (countOfChars % 2)
return NULL;
for (i = 0; i < (countOfChars>>1); i++) {
loc[0] = strchr( sel, str[2*i] );
loc[1] = strchr( sel, str[ ( 2*i ) + 1 ] );
if (loc[0] == NULL || loc[1] == NULL)
return NULL;
n[0] = (unsigned char)( loc[0] - sel );
n[1] = 23 - (unsigned char)( loc[1] - sel );
buf[i] = (unsigned char)((n[0] << 4) | n[1]);
}
return buf;
}后来由于项目需要，我特地改写了C#版。
public static class Base24
{
private static string sel = "BCDFGHJKMPQRTVWXY2346789";
public static string Encode(string Text)
{
int i = 0;
int Pos = 0;
char []Buf = new char[Text.Length<<1];
while ((i = Pos) < Text.Length)
{
Buf[i<<1] = sel[(Text[Pos]) >> 4];
Buf[(i<<1) + 1] = sel[23 - (Text[Pos] & 0x0F)];
Pos++;
}
return new string(Buf);
}
public static string Decode(string Text)
{
if (Text.Length % 2 != 0)
return null;
int [] NPos = new int[2];
char[] N = new char[2];
char[] Buf = new char[Text.Length >> 1];
for (int i = 0; i < (Text.Length >> 1); i++)
{
NPos[0] = sel.IndexOf(Text[ i<<1 ]);
NPos[1] = 23 - sel.IndexOf(Text[(i<<1) + 1]);
if (NPos[0] < 0 || NPos[1] < 0) {
return null;
}
Buf[i] = ((char)((NPos[0] << 4) | NPos[1]));
}
return new string(Buf);
}
}- Base64 : Base64是网络上最常见的用于传输8Bit字节代码的编码方式之一。 [更多]