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From: ts@cup.portal.com (Tim W Smith)
Newsgroups: comp.arch
Subject: Re: Bitfield instructions--a good idea?
Message-ID: <41313@cup.portal.com>
Date: 16 Apr 91 03:24:17 GMT
References: <1991Apr15.193425.3436@waikato.ac.nz> <3339@crdos1.crd.ge.COM>
Organization: The Portal System (TM)
Lines: 14

I know that the reason bitfield instructions were listed in the
early 386 documentation and then disappeared in later documents
was because the guy who was writing the Unix C compiler for the
386 port told Intel that his compiler would *never* *ever* use
these instructions because, once you took into account having to
get everything into the right registers, these instructions were
slower and took more code space than doing it with shifts and
masks.

So, given the choice of finishing debugging the microcode for
instructions that were not going to be used, or by taking them
out, Intel took them out.

						Tim Smith