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Q79286: FIX: Nested NOT Operators Yield Incorrect Value

Article: Q79286
Product(s): Microsoft Macro Assembler
Version(s): 6.0,6.0a,6.0b
Operating System(s): 
Keyword(s): 
Last Modified: 06-MAY-2001

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The information in this article applies to:

- Microsoft Macro Assembler (MASM), versions 6.0, 6.0a, 6.0b 
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SYMPTOMS
========

If the NOT operator is used more than once in an expression in the Microsoft
Macro Assembler (MASM), an incorrect value may be generated. For example:

  mov ax, not(not 0Fh)

incorrectly generates:

  mov ax, FFF1h

RESOLUTION
==========

To work around this, avoid using consecutive NOT operators. Using two NOT
operators is equivalent to using none.

STATUS
======

Microsoft has confirmed this to be a problem in MASM versions 6.0, 6.0a, and
6.0b. This problem was corrected in MASM for MS-DOS version 6.1.

MORE INFORMATION
================

Since the NOT operator should perform a bitwise or logical NOT operation, two
consecutive NOTs should produce the original number. The sample code below
demonstrates the problem.

Sample Code
-----------

  ; Assemble options needed:  none

  .MODEL small
  .STACK 4096

  .CODE
      .startup
      mov ax, not(not 0fh)
      .exit 0
  END

Additional query words: 6.00 6.00a 6.00b buglist6.00 buglist6.00a buglist6.00b fixlist6.10

======================================================================
Keywords          :  
Technology        : kbMASMsearch kbAudDeveloper kbMASM600 kbMASM600a kbMASM600b
Version           : :6.0,6.0a,6.0b
Solution Type     : kbfix

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