🚀 go-pugleaf

In <mostert.51@cs.sun.ac.za> mostert@cs.sun.ac.za (A. Mostert) writes:
>Hi all

>I just became aware of an undocumented instruction that (I think) works on
>all members of the x86 family. The opcode is D4 10 and it does this:
>   AH = AL >> 4
>   AL = AL & 0xF
>Is this a well known instruction ? Does anyone know of any other instructions
>(besides LOADALL and the 386 bit string stuff) that Intel did not tell us
>about ?

What you discovered was some time ago mentioned in the german computer magazine
"c't". (I guess is more an old story.)
This is the fact that the instructions 'aam' and 'aax' also work
with other basises then 10. It's sometimes (e.g. for conversions) very useful
and I use often following macros (turbo assembler):

aamx    MACRO basis             ;ah := al / basis
        db 0D4h, basis          ;al := al mod basis
        ENDM

aadx    MACRO basis             ;al := ah*basis + al
        db 0D5h, basis          ;ah := 0
        ENDM


You can then use it with (e.g.):

        aamx 16

regards,
Thomas

PS: What is the '386 bit string stuff'?
	
-- 
  Thomas Wolfram, European Advanced Networking Test Center
  (Process Computing Center, Technical University of Berlin)
  Strasse des 17.Juni 135, 1000 Berlin 12, Germany
  +49 030 31421294, wolf@prz.tu-berlin.de, thomas@aeon.in-berlin.de