HiWords and LoWords from Long Values
When translating C code to VB, you quite often come across the HiWord and LoWord operators, used to pack two integers into a long value. A simple translation of HiWord code will run into difficulties when unsigned integer arithmetic is being
used in the C code and the highest bit of the long value can be set. Since VB doesn't support unsigned arithmetic we have to strip out the high bit and add it back again later to avoid overflows and misleading results.
（当把C代码翻译到VB时，你经常会遇到高字和低字的操作，通常是把两个整型值合成一个长整型。当在C代码中使用了无符号整型，这最高一位是可以被设置的，因此简单的直接转换高字将会遇到困难。由于VB不支持无符号算术符，我们只好剥去这最高一位，在稍后再把它加回来，以避免溢出和错误的结果。）
Start a new project then add a class module. Add the following code to the module:
（开始一个新工程，增添一个类模块。把以下代码写入模块：）
Public Property Get LoWord(ByRef lThis As Long) As Long
LoWord = (lThis And &HFFFF&)
End Property
Public Property Let LoWord(ByRef lThis As Long, ByVal lLoWord As Long)
lThis = lThis And Not &HFFFF& Or lLoWord
End Property
Public Property Get HiWord(ByRef lThis As Long) As Long
If (lThis And &H80000000) = &H80000000 Then
HiWord = ((lThis And &H7FFF0000) \ &H10000) Or &H8000&
Else
HiWord = (lThis And &HFFFF0000) \ &H10000
End If
End Property
Public Property Let HiWord(ByRef lThis As Long, ByVal lHiWord As Long)
If (lHiWord And &H8000&) = &H8000& Then
lThis = lThis And Not &HFFFF0000 Or ((lHiWord And &H7FFF&) * &H10000) Or &H80000000
Else
lThis = lThis And Not &HFFFF0000 Or (lHiWord * &H10000)
End If
End Property
调用时，假定类模块取名CHiLo
Dim chl As New CHiLo
Dim a As Long
chl.LoWord(a) = &HFFFF0
chl.HiWord(a) = &HFFFF1
Me.Caption = Hex(a)
如此便可以正确无误地将高字和低字合成在一起。
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