Microsoft KB Archive/26624

Invalid BSF MASM Instruction Assembles Incorrectly ID Number: Q26624

5.00 MS-DOS

Summary:

The following two instructions are not valid MASM instructions:

BSF AX,EAX BSF AX,VAR1

The variable “VAR1” is a 32-bit variable. The “BSF AX,EAX” instruction encodes incorrectly to “0F BC C1” (which is the correct encoding for “BSF AX,CX”). The “BSF AX,VAR1” instruction encodes incorrectly to “0F BC 05 00000000” (the correct encoding for “BSFeax,VAR1”).

This feature is under review and will be considered for inclusion in a future release.