'**************************************************************
' Software name: PowerEasy SiteWeaver
' Web: http://www.powereasy.net
' Copyright (C) 2005－2008 佛山市動易網(wǎng)絡(luò)科技有限公司 版權(quán)所有
'**************************************************************

Const BASE_64_CHARACTERS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
Private sBASE_64_CHARACTERS

Public Function Base64encode(ByVal asContents)
asContents = strUnicode2Ansi(asContents)

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 len1 < 1 Then
Base64encode = ""
Exit Function
End If

M4 = len1 Mod 3
If M4 > 0 Then asContents = asContents & String(3 - M4, Chr(0))
'補(bǔ)足位數(shù)是為了便于計算

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

'處理最后剩余的幾個字符
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=號補(bǔ)足位數(shù)
Else
lsGroup64 = Char1 & Char2 & Char3 & ChrB(61) '用=號補(bǔ)足位數(shù)
End If

lsResult = lsResult & lsGroup64
End If

Base64encode = strAnsi2Unicode(lsResult)

End Function

Public Function Base64decode(ByVal asContents)
asContents = strUnicode2Ansi(asContents)

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(yīng)當(dāng)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

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

'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(zhuǎn)換成值為0
If M4 = 2 Then '補(bǔ)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 = strAnsi2Unicode(lsResult)

End Function

Private Function strUnicodeLen(ByVal asContents)
'計算unicode字符串的Ansi編碼的長度
Dim asContents1
Dim len1
Dim k
Dim i
Dim 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

Private Function strUnicode2Ansi(ByVal asContents)
'將Unicode編碼的字符串，轉(zhuǎn)換成Ansi編碼的字符串
Dim len1
Dim i
Dim VarChar
Dim varAsc
Dim 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

Private Function strAnsi2Unicode(asContents)
'將Ansi編碼的字符串，轉(zhuǎn)換成Unicode編碼的字符串
Dim len1
Dim i
Dim VarChar
Dim 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