FIX: Relational Operators Evaluate to Wrong Value

The information in this article applies to:

• Microsoft Macro Assembler for MS-DOS, versions 5.0, 5.1, and 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

The following demonstrates this problem with MASM 5.0:

Sample Code

              .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

              .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