Const BASE_64_CHARACTERS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
Private sBASE_64_CHARACTERS
Function Base64encode(ByVal asContents)
asContents = strUnicode2Ansi(asContents)
Dim lnPosition,lsResult,Char1,Char2,Char3,Char4,Byte1,Byte2,Byte3,SaveBits1,SaveBits2,lsGroupBinary,lsGroup64,M4, len1, len2
len1 = LenB(asContents)
If len1 < 1 Then
Base64encode = ""
Exit Function
End If
M4 = len1 Mod 3
If M4 > 0 Then asContents = asContents & String(3 - M4, Chr(0))
'补足位数是为了便于计算
If M4 > 0 Then
len1 = len1 + (3 - M4)
len2 = len1 - 3
Else
len2 = len1
End If
lsResult = ""
sBASE_64_CHARACTERS = strUnicode2Ansi(BASE_64_CHARACTERS)
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 M4 > 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 M4 = 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 = strAnsi2Unicode(lsResult)
End Function
Function Base64decode(ByVal asContents)
asContents = strUnicode2Ansi(asContents)
Dim lsResult,lnPosition,lsGroup64, lsGroupBinary,Char1, Char2, Char3, Char4,Byte1, Byte2, Byte3,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
sBASE_64_CHARACTERS = strUnicode2Ansi(BASE_64_CHARACTERS)
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 = strAnsi2Unicode(lsResult)
End Function
Function strUnicodeLen(ByVal asContents)
'计算unicode字符串的Ansi编码的长度
Dim asContents1
Dim len1,k,i,asc1
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(ByVal asContents)
'将Unicode编码的字符串,转换成Ansi编码的字符串
Dim len1,i,VarChar,varAsc,varHex, varlow, varhigh
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
Dim len1,i,VarChar,varAsc
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