Asp base64编码、解码函数

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

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