🚀 go-pugleaf

Jari 'jja' Ahola writes:
>
> What has happened to 80386's opcodes IBTS and XBTS (insert and extract
> bit streams)?  Masm 5.0 recognizes the opcodes, but doesn't generate
> the right code.  Has this been fixed in MASM 5.X or are these opcodes no
> longer supported in 80386?
>

     I just got off the phone with Intel, and the technical representative
claimed no knowledge of the instructions.  Just moments after that however,
I was thumbing through "Advanced 80386 Programming Techniques" by
James L. Turley, and found this in a section called "Evolution of the
80386" (pp 487-498):

     "IBTS and XBTS Instructions Removed.  The Insert Bit String (IBTS)
and Extract Bit String (XBTS) instructions were removed from the 80386
instruction set.  It was determined that they took up too much space on
the microprocessor and that their functionality could be duplicated with
the SHLD and SHRD instructions.  The opcodes 0FA6 and 0FA7 now produce
invalid opcode faults."

     I tried compiling XBTS and IBTS in MASM 5.1 and it compiled fine,
but if you look at the code with CodeView (tm) then you will find invalid
opcodes in their place (0F).  Apparently, Microsoft left in recognition of
the mnemonics, but no longer compiles the opcodes.  Makes you wonder about
Microsoft sometimes doesn't it?  (Especially considering I reported about
6 bugs last week in MASM alone.)

-- 
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