Using the Imp Operator for Binary Comparison (168344)

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Microsoft provides programming examples for illustration only, without warranty either expressed or implied. This includes, but is not limited to, the implied warranties of merchantability or fitness for a particular purpose. This article assumes that you are familiar with the programming language that is being demonstrated and with the tools that are used to create and to debug procedures. Microsoft support engineers can help explain the functionality of a particular procedure, but they will not modify these examples to provide added functionality or construct procedures to meet your specific requirements. The syntax for the Imp operator is as follows where <expression1> and <expressions2> are any expressions and <result> is any numeric variable.

When you use the Imp operator to perform a bit-wise comparison of identically positioned bits in two numeric expressions, the result of the bit-wise comparison is determined using the rules in the following table.

   Bit in Expression1   Bit in Expression2   Bit in Result
   -------------------------------------------------------
           1                     1                 1
           1                     0                 0
           0                     1                 1
           0                     0                 1
				

For example, if you run the following macro, a message box displays the value of -11:

   Sub Imp_Example()
 
   Dim a As Integer
   Dim b As Integer
   Dim result As Integer
 
      a =10
      b = 4
 
      result = a Imp b
 
      MsgBox result
 
   End Sub
				

The value -11 is returned because the macro follows the rules in the table and uses twos complement notation. Using twos complement notation, the leftmost bit represents the sign bit. If this bit is one, the number is negative; if this bit is zero, the number is positive. To convert a negative number from binary back to decimal, complement all of the bits (1 becomes 0 and 0 becomes 1), convert that number to decimal, change the sign of the decimal number, and then subtract 1.

In the example, the Imp operator is used with the two numeric values 10 and 4. In binary form (2 bytes), these two numbers appear as follows: Using the bit-wise comparison rules from the table yields the result value in binary form:

   10:   0000000000001010
    4:   0000000000000100
   --------------------------

   result:   1111111111110101
				

To determine the decimal equivalent of result, use the twos complement rules of conversion as follows:

                                     Result: 1111111111110101
                        Complement each bit: 0000000000001010
 
   Decimal equivalent of this binary number: 10
 
                    Opposite of this number: -10
       Subtract 1 (decimal value of result): -11