Sign-Extended Register and Immediate from of AND/OR/XOR

ID: Q31598

The information in this article applies to:

Microsoft Macro Assembler for MS-DOS, versions 5.0, 5.1, 6.0
Microsoft Macro Assembler for OS/2, versions 5.1, 6.0

SUMMARY

The Microsoft Macro Assembler will generate sign-extended encodings whenever possible. The following are MASM instructions that will produce sign-extended encodings:


Assembler           Sign-Extended               Nonsign-Extended
Instructions        Encodings                   Encodings

AND bx, 0ffffh      83 E3 FF                    81 E3 FFFF
ADD bx, 0001h       83 C3 01                    81 C3 0001
ADC bx, 0fh         83 D3 0F                    81 D3 000F
OR  bx, 1           83 CB 01                    81 CB 0001
SBB bx, 0ffffh      83 DB FF                    81 DB FFFF
SUB bx, 3           83 EB 03                    81 EB 0003
XOR bx, 0002h       83 F3 02                    81 F3 0002
CMP bx, 0fff2h      83 FB F2                    81 FB FFF2

MORE INFORMATION

MASM will choose the sign-extended version of the instruction because of the 1-byte savings in the encoding. The 8088/8086/80186/80286 processors do support the sign-extended encoding, but documentation on this feature is limited. The support of sign-extended encoding is documented in the "8086/8088/80186/80188 Programmer's Pocket Reference Guide" on Page 43.

Additional query words: kbinf 5.00 5.10 6.00

Keywords :
Version : :5.0,5.1,6.0
Platform :
Issue type :