FIX: Relational Operators Evaluate to Wrong Value

ID: Q26822

The information in this article applies to:

Microsoft Macro Assembler for MS-DOS, versions 5.0, 5.1, 5.1a

SYMPTOMS

When used with a MOV instruction, some relational operators will evaluate to the wrong value. The following listing file sections are examples of this problem. It is important to note that FFFF = true, and 0000 = false. It is also important to note that when FFFFh is used with the GT, GE, or LT, LE operator, it is interpreted as the largest positive number and not as -1.

STATUS

Microsoft has confirmed this to be a problem in Microsoft Macro Assembler (MASM) version 5.0, 5.1, and 5.1a. This problem was corrected in MASM version 6.0.

MORE INFORMATION

Sample Code

The following demonstrates this problem with MASM 5.0:


              .MODEL SMALL
       0000   .CODE
       0000   B8 0000    MOV AX, 0FFFFH GT -1
       0003   B8 FFFF    MOV AX, 0FFFFH LE -1
       0006

              .386
              .MODEL SMALL
       0000   .CODE
       0000   66 | B8 FFFF   MOV AX, -1 GE 0FFFFFFFFH
       0004   66 | B8 FFFF   MOV AX, 0FFFFFFFFH LE -1
       0008   66 | B8 0000   MOV AX, 0FFFFFFFFH GT -1
       000C   66 | B8 0000   MOV AX, -1 LT 0FFFFFFFFH
       0010   END

The following demonstrates the problem MASM 5.1:


              .MODEL SMALL
       0000   .CODE
       0000   B8 0000    MOV AX, 0FFFFH GT -1
       0003   B8 FFFF    MOV AX, 0FFFFH LE -1
       0006

              .386
              .MODEL SMALL
       0000   .CODE
       0000   66 | B8 FFFF   MOV AX, -1 GE 0FFFFFFFFH
       0004   66 | B8 0000   MOV AX, 0FFFFFFFFH LE -1
       0008   66 | B8 FFFF   MOV AX, 0FFFFFFFFH GT -1
       000C   66 | B8 0000   MOV AX, -1 LT 0FFFFFFFFH
       0010   END

Additional query words: 5.00 5.10 5.10a buglist5.00 buglist5.10 fixlist6.00

Keywords :
Version : :5.0,5.1,5.1a
Platform :
Issue type :