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在C和Java等编程语言中，可以方便地对变量进行移位运算，但是在VB中，却没有内置的移位运算符或者函数。
于是，我们得自己动手编写移位的运算函数。原理很简单，每向右移一位，就将被移位的变量的二进制除以2；每向左移一位，就将被移位的变量的二进制乘以2。于是可以写出以下函数：
'
' 按位左移
'
Public Function LShift(ByVal val, ByVal n)
LShift = val * 2 ^ n
End Function
'
' 按位右移
'
Public Function RShift(ByVal val, Byval n)
RShift = val \ (2 ^ n)
End Function
以上写的两个左移和右移函数，非常简单，没有考虑机器字长以及传过来的变量类型等。
后来看到在VBS的MD5加密算法中，包含左移右移的函数，在这里，将它们单独拧出来，以作为左移右移函数的升级版本：
Private m_lOnBits(30) Private m_l2Power(30)Private Function Initialize() m_lOnBits(0) = CLng(1) m_lOnBits(1) = CLng(3) m_lOnBits(2) = CLng(7) m_lOnBits(3) = CLng(15) m_lOnBits(4) = CLng(31) m_lOnBits(5) = CLng(63) m_lOnBits(6) = CLng(127) m_lOnBits(7) = CLng(255) m_lOnBits(8) = CLng(511) m_lOnBits(9) = CLng(1023) m_lOnBits(10) = CLng(2047) m_lOnBits(11) = CLng(4095) m_lOnBits(12) = CLng(8191) m_lOnBits(13) = CLng(16383) m_lOnBits(14) = CLng(32767) m_lOnBits(15) = CLng(65535) m_lOnBits(16) = CLng(131071) m_lOnBits(17) = CLng(262143) m_lOnBits(18) = CLng(524287) m_lOnBits(19) = CLng(1048575) m_lOnBits(20) = CLng(2097151) m_lOnBits(21) = CLng(4194303) m_lOnBits(22) = CLng(8388607) m_lOnBits(23) = CLng(16777215) m_lOnBits(24) = CLng(33554431) m_lOnBits(25) = CLng(67108863) m_lOnBits(26) = CLng(134217727) m_lOnBits(27) = CLng(268435455) m_lOnBits(28) = CLng(536870911) m_lOnBits(29) = CLng(1073741823) m_lOnBits(30) = CLng(2147483647) m_l2Power(0) = CLng(1) m_l2Power(1) = CLng(2) m_l2Power(2) = CLng(4) m_l2Power(3) = CLng(8) m_l2Power(4) = CLng(16) m_l2Power(5) = CLng(32) m_l2Power(6) = CLng(64) m_l2Power(7) = CLng(128) m_l2Power(8) = CLng(256) m_l2Power(9) = CLng(512) m_l2Power(10) = CLng(1024) m_l2Power(11) = CLng(2048) m_l2Power(12) = CLng(4096) m_l2Power(13) = CLng(8192) m_l2Power(14) = CLng(16384) m_l2Power(15) = CLng(32768) m_l2Power(16) = CLng(65536) m_l2Power(17) = CLng(131072) m_l2Power(18) = CLng(262144) m_l2Power(19) = CLng(524288) m_l2Power(20) = CLng(1048576) m_l2Power(21) = CLng(2097152) m_l2Power(22) = CLng(4194304) m_l2Power(23) = CLng(8388608) m_l2Power(24) = CLng(16777216) m_l2Power(25) = CLng(33554432) m_l2Power(26) = CLng(67108864) m_l2Power(27) = CLng(134217728) m_l2Power(28) = CLng(268435456) m_l2Power(29) = CLng(536870912) m_l2Power(30) = CLng(1073741824) End Function
Private Function LShift(lValue, iShiftBits) If iShiftBits = 0 Then LShift = lValue Exit Function ElseIf iShiftBits = 31 Then If lValue And 1 Then LShift = &H80000000 Else LShift = 0 End If Exit Function ElseIf iShiftBits < 0 Or iShiftBits > 31 Then Err.Raise 6 End If
If (lValue And m_l2Power(31 - iShiftBits)) Then LShift = ((lValue And m_lOnBits(31 - (iShiftBits + 1))) m_l2Power(iShiftBits)) Or &H80000000 Else LShift = ((lValue And m_lOnBits(31 - iShiftBits)) m_l2Power(iShiftBits)) End If End Function
Private Function RShift(lValue, iShiftBits) If iShiftBits = 0 Then RShift = lValue Exit Function ElseIf iShiftBits = 31 Then If lValue And &H80000000 Then RShift = 1 Else RShift = 0 End If Exit Function ElseIf iShiftBits < 0 Or iShiftBits > 31 Then Err.Raise 6 End If RShift = (lValue And &H7FFFFFFE) m_l2Power(iShiftBits)
If (lValue And &H80000000) Then RShift = (RShift Or (&H40000000 m_l2Power(iShiftBits - 1))) End If End Function
另外，在此基础上再添加两个位运算函数：循环左移和无符号数的加法运算。
Private Function RotateLeft(lValue, iShiftBits) RotateLeft = LShift(lValue, iShiftBits) Or RShift(lValue, (32 - iShiftBits)) End FunctionPrivate Function AddUnsigned(lX, lY) Dim lX4 Dim lY4 Dim lX8 Dim lY8 Dim lResult lX8 = lX And &H80000000 lY8 = lY And &H80000000 lX4 = lX And &H40000000 lY4 = lY And &H40000000 lResult = (lX And &H3FFFFFFF) + (lY And &H3FFFFFFF) If lX4 And lY4 Then lResult = lResult Xor &H80000000 Xor lX8 Xor lY8 ElseIf lX4 Or lY4 Then If lResult And &H40000000 Then lResult = lResult Xor &HC0000000 Xor lX8 Xor lY8 Else lResult = lResult Xor &H40000000 Xor lX8 Xor lY8 End If Else lResult = lResult Xor lX8 Xor lY8 End If AddUnsigned = lResult End Function