FIX: Relational Operators with MOV May Evaluate Incorrectly

The information in this article applies to:

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

SYMPTOMS

In the Microsoft Macro Assembler (MASM) versions 5.0, 5.1, and 5.1a, some of the relational operators evaluate to the wrong value when used with a MOV instruction.

STATUS

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

MORE INFORMATION

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, LE, and LT operators, it is interpreted as the largest positive number, not as -1.

Sample Listing File

1                                .MODEL SMALL
2                                .CODE
3 0000  B8 0000                  MOV AX, 0FFFFH GT -1
4 0003  B8 FFFF                  MOV AX, 0FFFFH LE -1
5                                END

1                                .386
2                                .MODEL SMALL
3                                .CODE
4 0000  66| B8 FFFF              MOV AX, -1  GE  0FFFFFFFFH
5 0004  66| B8 FFFF              MOV AX, 0FFFFFFFFH  LE  -1
6 0008  66| B8 0000              MOV AX, 0FFFFFFFFH  GT  -1
7 000C  66| B8 0000              MOV AX, -1  LT  0FFFFFFFFH
8                                END