6 Feb
2008
6 Feb
'08
10:29 a.m.
Date: Tue, 05 Feb 2008 20:25:07 -0500
From: Allison
Maufacturing no. Design yes. back then there was
little if any automated
chip design so anything to save time or transistors on the die was good.
The redundant moves are simple example of not decoding all possible
states. Saves transistors at a time when getting things on that much
silicon was still hard.
My point was "documentation" of these instructions as such was
unnecessary. Had the documentation simply said "---", they wouldn't
have been used, freeing the codes for later exploitation. But once
documented as valid moves, there's no going back.
00H was the only *documented* no-op as such.
But it's all 20-20 hindsight.
Cheers,
Chuck