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From: cs450a03@uc780.umd.edu
Newsgroups: comp.arch
Subject: RE: Bitfield and loop instructions--a good idea?
Message-ID: <15APR91.22405995@uc780.umd.edu>
Date: 15 Apr 91 22:40:59 GMT
References: <1991Apr15.193425.3436@waikato.ac.nz> <2302@spim.mips.COM>
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Zalman Stern writes:
>    rrib	Takes bit 0 of source register, rotates it by an amount in
>		a register and inserts it into the destination register.
>		(I'm not sure what this is used for.)

That's for setting up bit arrays where you're applying some predicate
to a large quantity of data.

>All in all this stuff is neat and adds character to the architecture.
>However, I'm not sure it is the best way to do things. Some codes
>will perform better due to the bit manipulation instructions, but I
>doubt they show up very often at all.

They don't in programs written in C.  C has no support for generic bit
crunching.  (The same goes for FORTRAN, and so on...)

Raul Rockwell