<%
dim sBASE_64_CHARACTERS
dim len1,k
dim asc1,asContents1
dim varchar,varasc,varHex,varlow,varhigh
sBASE_64_CHARACTERS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"  
sBASE_64_CHARACTERS = strUnicode2Ansi(sBASE_64_CHARACTERS)

Function strUnicodeLen(asContents)
  '计算unicode字符串的Ansi编码的长度
  asContents1="a"&asContents
  len1=len(asContents1)
  k=0
  for i=1 to len1
      asc1=asc(mid(asContents1,i,1))
      if asc1<0 then asc1=65536+asc1
      if asc1>255 then
         k=k+2
      else
         k=k+1
      end if
  next
  strUnicodeLen=k-1
End Function

Function strUnicode2Ansi(asContents)
  '将Unicode编码的字符串，转换成Ansi编码的字符串
  strUnicode2Ansi=""
  len1=len(asContents)
  for i=1 to len1
      varchar=mid(asContents,i,1)
      varasc=asc(varchar)
      if varasc<0 then varasc=varasc+65536
      if varasc>255 then
         varHex=Hex(varasc)
         varlow=left(varHex,2)
         varhigh=right(varHex,2)
         strUnicode2Ansi=strUnicode2Ansi & chrb("&H" & varlow ) & chrb("&H" & varhigh )
      else
         strUnicode2Ansi=strUnicode2Ansi & chrb(varasc)
      end if
   next
End function

Function strAnsi2Unicode(asContents)
  '将Ansi编码的字符串，转换成Unicode编码的字符串
  strAnsi2Unicode = ""
  if isnull(asContents) or asContents="" then exit function
  len1=lenb(asContents)
  if len1=0 then exit function
  for i=1 to len1
      varchar=midb(asContents,i,1)
      varasc=ascb(varchar)
      if varasc > 127  then
     if midb(asContents,i+1,1)<>"" then
         strAnsi2Unicode = strAnsi2Unicode & chr(ascw(midb(asContents,i+1,1) & varchar))
 end if
         i=i+1
      else
         strAnsi2Unicode = strAnsi2Unicode & chr(varasc)
      end if
  next
End function

Function Base64encode(asContents)  
'将Ansi编码的字符串进行Base64编码
'asContents应当是ANSI编码的字符串（二进制的字符串也可以）
Dim lnPosition  
Dim lsResult  
Dim Char1  
Dim Char2  
Dim Char3  
Dim Char4  
Dim Byte1  
Dim Byte2  
Dim Byte3  
Dim SaveBits1  
Dim SaveBits2  
Dim lsGroupBinary  
Dim lsGroup64  
Dim m3,m4,len1,len2

len1=Lenb(asContents)
if len1<1 then 
   Base64encode=""
   exit Function
end if

m3=Len1 Mod 3 
If M3 > 0 Then asContents = asContents & String(3-M3, chrb(0))  
'补足位数是为了便于计算

IF m3 > 0 THEN 
   len1=len1+(3-m3)
   len2=len1-3
else
   len2=len1
end if

lsResult = ""  

For lnPosition = 1 To len2 Step 3  
    lsGroup64 = ""  
    lsGroupBinary = Midb(asContents, lnPosition, 3)  

    Byte1 = Ascb(Midb(lsGroupBinary, 1, 1)): SaveBits1 = Byte1 And 3  
    Byte2 = Ascb(Midb(lsGroupBinary, 2, 1)): SaveBits2 = Byte2 And 15  
    Byte3 = Ascb(Midb(lsGroupBinary, 3, 1))  

    Char1 = Midb(sBASE_64_CHARACTERS, ((Byte1 And 252) \ 4) + 1, 1)  
    Char2 = Midb(sBASE_64_CHARACTERS, (((Byte2 And 240) \ 16) Or (SaveBits1 * 16) And &HFF) + 1, 1)  
    Char3 = Midb(sBASE_64_CHARACTERS, (((Byte3 And 192) \ 64) Or (SaveBits2 * 4) And &HFF) + 1, 1)  
    Char4 = Midb(sBASE_64_CHARACTERS, (Byte3 And 63) + 1, 1)  
    lsGroup64 = Char1 & Char2 & Char3 & Char4  
    
    lsResult = lsResult & lsGroup64  
Next  

'处理最后剩余的几个字符
if M3 > 0  then
    lsGroup64 = ""  
    lsGroupBinary = Midb(asContents, len2+1, 3)  

    Byte1 = Ascb(Midb(lsGroupBinary, 1, 1)): SaveBits1 = Byte1 And 3  
    Byte2 = Ascb(Midb(lsGroupBinary, 2, 1)): SaveBits2 = Byte2 And 15  
    Byte3 = Ascb(Midb(lsGroupBinary, 3, 1))  

    Char1 = Midb(sBASE_64_CHARACTERS, ((Byte1 And 252) \ 4) + 1, 1)  
    Char2 = Midb(sBASE_64_CHARACTERS, (((Byte2 And 240) \ 16) Or (SaveBits1 * 16) And &HFF) + 1, 1)  
    Char3 = Midb(sBASE_64_CHARACTERS, (((Byte3 And 192) \ 64) Or (SaveBits2 * 4) And &HFF) + 1, 1)  

    if M3=1 then
       lsGroup64 = Char1 & Char2 & ChrB(61) & ChrB(61)   '用=号补足位数
    else
       lsGroup64 = Char1 & Char2 & Char3 & ChrB(61)      '用=号补足位数
    end if
    
    lsResult = lsResult & lsGroup64  
end if

Base64encode = lsResult  

End Function  


Function Base64decode(asContents)  
'将Base64编码字符串转换成Ansi编码的字符串
'asContents应当也是ANSI编码的字符串（二进制的字符串也可以）
Dim lsResult  
Dim lnPosition  
Dim lsGroup64, lsGroupBinary  
Dim Char1, Char2, Char3, Char4  
Dim Byte1, Byte2, Byte3  
Dim M4,len1,len2

len1= Lenb(asContents) 
M4 = len1 Mod 4

if len1 < 1 or M4 > 0 then
   '字符串长度应当是4的倍数
   Base64decode = ""  
   exit Function  
end if
       
'判断最后一位是不是 = 号
'判断倒数第二位是不是 = 号
'这里m4表示最后剩余的需要单独处理的字符个数
if midb(asContents, len1, 1) = chrb(61)   then   m4=3 
if midb(asContents, len1-1, 1) = chrb(61) then   m4=2

if m4 = 0 then
   len2=len1
else
   len2=len1-4
end if

For lnPosition = 1 To Len2 Step 4  
    lsGroupBinary = ""  
    lsGroup64 = Midb(asContents, lnPosition, 4)  
    Char1 = InStrb(sBASE_64_CHARACTERS, Midb(lsGroup64, 1, 1)) - 1  
    Char2 = InStrb(sBASE_64_CHARACTERS, Midb(lsGroup64, 2, 1)) - 1  
    Char3 = InStrb(sBASE_64_CHARACTERS, Midb(lsGroup64, 3, 1)) - 1  
    Char4 = InStrb(sBASE_64_CHARACTERS, Midb(lsGroup64, 4, 1)) - 1  
    Byte1 = Chrb(((Char2 And 48) \ 16) Or (Char1 * 4) And &HFF)  
    Byte2 = lsGroupBinary & Chrb(((Char3 And 60) \ 4) Or (Char2 * 16) And &HFF)  
    Byte3 = Chrb((((Char3 And 3) * 64) And &HFF) Or (Char4 And 63))  
    lsGroupBinary = Byte1 & Byte2 & Byte3  
    
    lsResult = lsResult & lsGroupBinary  
Next 

'处理最后剩余的几个字符
if M4 > 0 then 
    lsGroupBinary = ""  
    lsGroup64 = Midb(asContents, len2+1, m4) & chrB(65)   'chr(65)=A，转换成值为0
    if M4=2 then                                          '补足4位，是为了便于计算 
        lsGroup64 = lsGroup64 & chrB(65)                  
    end if
    Char1 = InStrb(sBASE_64_CHARACTERS, Midb(lsGroup64, 1, 1)) - 1  
    Char2 = InStrb(sBASE_64_CHARACTERS, Midb(lsGroup64, 2, 1)) - 1  
    Char3 = InStrb(sBASE_64_CHARACTERS, Midb(lsGroup64, 3, 1)) - 1  
    Char4 = InStrb(sBASE_64_CHARACTERS, Midb(lsGroup64, 4, 1)) - 1  
    Byte1 = Chrb(((Char2 And 48) \ 16) Or (Char1 * 4) And &HFF)  
    Byte2 = lsGroupBinary & Chrb(((Char3 And 60) \ 4) Or (Char2 * 16) And &HFF)  
    Byte3 = Chrb((((Char3 And 3) * 64) And &HFF) Or (Char4 And 63))  
  
    if M4=2 then
       lsGroupBinary = Byte1
    elseif M4=3 then
       lsGroupBinary = Byte1 & Byte2
    end if
    
    lsResult = lsResult & lsGroupBinary  
end if

Base64decode = lsResult  

End Function  
%>
