用VB实现一个简单的ESMTP客户端

p;         c1 = base64DecodeChars(Asc(Mid(str, i + 1, 1)) And 255)
            i = i + 1
        Loop While (i < len1 And c1 = -1)
        If (c1 = -1) Then
            base64decode = out
            Exit Function
        End If
   
        Do
            c2 = base64DecodeChars(Asc(Mid(str, i + 1, 1)) And 255)
            i = i + 1
        Loop While (i < len1 And c2 = -1)
        If (c2 = -1) Then
            base64decode = out
            Exit Function
        End If
        out = out + Chr((c1 * 4) Or ((c2 And 48) \ 16))

        Do
            c3 = base64DecodeChars(Asc(Mid(str, i + 1, 1)) And 255)
            i = i + 1
            If (c3 = 61) Then
                base64decode = out
                c3 = base64DecodeChars(c3)
            End If
        Loop While (i < len1 And c3 = -1)
        If (c3 = -1) Then
            base64decode = out
            Exit Function
        End If
        out = out + Chr(((c2 And 15) * 16) Or ((c3 And 60) \ 4))

        Do
            c4 = base64DecodeChars(Asc(Mid(str, i + 1, 1)) And 255)
            i = i + 1
            If (c4 = 61) Then
                base64decode = out