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sBASE_64_CHARACTERS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
sBASE_64_CHARACTERS = strUnicode2Ansi(sBASE_64_CHARACTERS)

Function strUnicodeLen(asContents)
'計算unicode字符串的Ansi編碼的長度
asContents1="a"asContents
len1=len(asContents1)
k=0
for i=1 to len1
asc1=asc(mid(asContents1,i,1))
if asc10 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)
'將Unicode編碼的字符串，轉換成Ansi編碼的字符串
strUnicode2Ansi=""
len1=len(asContents)
for i=1 to len1
varchar=mid(asContents,i,1)
varasc=asc(varchar)
if varasc0 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)
'將Ansi編碼的字符串，轉換成Unicode編碼的字符串
strAnsi2Unicode = ""
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
strAnsi2Unicode = strAnsi2Unicode chr(ascw(midb(asContents,i+1,1) varchar))
i=i+1
else
strAnsi2Unicode = strAnsi2Unicode chr(varasc)
end if
next
End function

Function Base64encode(asContents)
'將Ansi編碼的字符串進行Base64編碼
'asContents應當是ANSI編碼的字符串（二進制的字符串也可以）
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 m4,len1,len2

len1=Lenb(asContents)
if len11 then
Base64encode=""
exit Function
end if

m3=Len1 Mod 3
If M3 > 0 Then asContents = asContents String(3-M3, chrb(0))
'補足位數(shù)是為了便于計算

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

'處理最后剩余的幾個字符
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=號補足位數(shù)
else
lsGroup64 = Char1 Char2 Char3 ChrB(61) '用=號補足位數(shù)
end if

lsResult = lsResult lsGroup64
end if

Base64encode = lsResult

End Function


Function Base64decode(asContents)
'將Base64編碼字符串轉換成Ansi編碼的字符串
'asContents應當也是ANSI編碼的字符串（二進制的字符串也可以）
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
'字符串長度應當是4的倍數(shù)
Base64decode = ""
exit Function
end if

'判斷最后一位是不是 = 號
'判斷倒數(shù)第二位是不是 = 號
'這里m4表示最后剩余的需要單獨處理的字符個數(shù)
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

'處理最后剩余的幾個字符
if M4 > 0 then
lsGroupBinary = ""
lsGroup64 = Midb(asContents, len2+1, m4) chrB(65) 'chr(65)=A，轉換成值為0
if M4=2 then '補足4位，是為了便于計算
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
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