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From: John Savard <quadibloc@servername.invalid>
Newsgroups: comp.arch
Subject: Re: "Mini" tags to reduce the number of op codes
Date: Thu, 04 Apr 2024 21:13:13 -0600
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On some older CPUs, there might be one set of integer opcodes and one
set of floating-point opcodes, with a status register containing the
integer precision, and the floating-point precision, currently in use.

The idea was that this would be efficient because most programs only
use one size of each type of number, so the number of opcodes would be
the most appropriate, and that status register wouldn't need to be
reloaded too often.

It's considered dangerous, though, to have a mechanism for changing
what instructions mean, since this could let malware alter what
programs do in a useful and sneaky fashion. Memory bandwidth is no
longer a crippling constraint the way it was back in the days of core
memory and discrete transistors - at least not for program code, even
if memory bandwidth for _data_ often limits the processing speed of
computers.

This is basically because any program that does any real work, taking
any real length of time to do its job, is going to mostly consist of
loops that fit in cache. So letting program code be verbose if there
are other benefits obtained thereby is the current conventional
wisdom.

John Savard