Path: csiph.com!eternal-september.org!feeder.eternal-september.org!nntp.eternal-september.org!.POSTED!not-for-mail From: Tim Rentsch Newsgroups: comp.arch Subject: Re: Flags (Re: arithmetic and endian history) Date: Thu, 01 Oct 2026 06:49:57 -0700 Organization: A noiseless patient Spider Lines: 22 Message-ID: <86tsn5pm2i.fsf@linuxsc.com> References: <10uks4f$1dqo$1@gal.iecc.com> <119en6p$qve$1@gal.iecc.com> <2026Sep29.100113@mips.complang.tuwien.ac.at> <1790702502-5857@newsgrouper.org> <119h6a0$fiu$1@gal.iecc.com> <2026Oct1.110046@mips.complang.tuwien.ac.at> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Injection-Date: Thu, 01 Oct 2026 13:50:00 +0000 (UTC) Injection-Info: dont-email.me; logging-data="1275193"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/VCgcrFSRAEJEUaZ6xxEQrbLkUaSM+E/I="; posting-host="18a74afe15b7c222d977d31c18068e17" User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.4 (gnu/linux) Cancel-Lock: sha1:S2C6ASGRedDIycg0VqXX2Vj0dZk= sha1:hL818qEmcMYe+Md2/BwBkR47Tk4= sha256:/0ajun9rIxhvQuNpUnYpUHpADV8Cdh/ABvNMWfcHvOM= sha1:b2ZvFLN/AO0eIv0Yx0RrK+hWE1E= sha256:4ytXRvp4qlDrUzOmkUVpgzK+CqZ0QBEecQPKIWsDBk4= Xref: csiph.com comp.arch:118349 anton@mips.complang.tuwien.ac.at (Anton Ertl) writes: > John Levine writes: > >> Re a different question about why they only had two encoded condtion >> code bits, I agree that it's because storage was expensive. The CC >> took up two bits in the program status word and every bit was >> precious. I also suspect that they looked at all of the conditions >> they wanted to report and found that there was never more than four >> for any particular instruction, so 2 bits was plenty. Remember that >> the BC instruction had a four bit mask so it could separately select >> each combination of the two bits. > > I suspect that the additional logic for the multiplexing of the > conditions on these two bits was more expensive than two additional > bits would have been. My guess is that they use these two bits > because 1) when you don't know any better, minimizing the number of > flag bits looks like a good idea, and 2) they did not know any > better. Do you really mean to suggest that Gene Amdahl, Gerrit Blaauw and Fred Brooks didn't know what they were doing?