My opinion (not substantiated by facts or reality):
The halfword versions of NIxx and OIxx were done for an earlier
machine. When the time came to add the fullword versions such
as NIxF and OIxF (and XIxF), the CPU architectes realized that
there was no need for the halfword versions, as all the 16-bit
operations can be done just as well with 32-bit versions. Thus,
XILL 0,X'F000' and XILF 0,X'0000F000'
do the same thing, and similarly for AND and OR. Because the
halfword versions of N and O were already in the field and
couldn't be removed, only the fullword versions of X were added.
John Ehrman
(------------------ Referenced Note Follows --------------------)
Date: Wed, 1 Aug 2012 12:32:47 -0400
From: Thomas David Rivers <[email protected]>
Binyamin Dissen wrote:
>NILL? check. OILL? check. XILL? not present
>
>Binyamin Dissen <[email protected]>
Maybe they were running out of acreage? But XOR
is very doable with a few NOTs, ANDs and ORs...
So, maybe it just wasn't worth the effort??
See http://en.wikipedia.org/wiki/Exclusive_or for a nice
write-up...
- Dave Rivers -
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