Re: adding overflow and carry to every GPR (was Re: OT: Epic RISC-V rant)

Path	csiph.com!eternal-september.org!feeder.eternal-september.org!nntp.eternal-september.org!.POSTED!not-for-mail
From	Kragen Javier Sitaker <kragen@canonical.org>
Newsgroups	comp.arch
Subject	Re: adding overflow and carry to every GPR (was Re: OT: Epic RISC-V rant)
Date	Wed, 02 Sep 2026 13:52:54 -0300
Organization	Primarily biological and memetic
Lines	16
Message-ID	<871pbb8ujd.fsf@debian> (permalink)
References	<87qzk0nejz.fsf@nightsong.com> <116d89d$27baf$1@paganini.bofh.team> <2026Aug24.095510@mips.complang.tuwien.ac.at> <87a4q0afu7.fsf_-_@debian> <20260901143106.00006dd7@gmail.com> <1788314691-5857@newsgrouper.org>
MIME-Version	1.0
Content-Type	text/plain
Injection-Date	Wed, 02 Sep 2026 16:52:58 +0000 (UTC)
Injection-Info	dont-email.me; logging-data="3127707"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/5zjdFqY9UD7gwBzdYzWLW"; posting-host="de81ddf0846fce2f7070364d1569cfb9"
User-Agent	Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux)
Cancel-Lock	sha1:EHtPb69Odi/4qRAucEKQGLOID3M= sha1:Er7ctocEiy2gTdNGArOBS/DnRi8= sha256:rKdbpA5RkQyVJNrTh0B/DWXC62y7/dCfcYVvdLLIOj8= sha1:n4IJry4IjkMh2yc+tTeoSe/vTeM= sha256:6sCNDSMAMGI9Cqls4n9cQ+HNm63VMuGoHy8zWgrnFJo=
Xref	csiph.com comp.arch:117738

Show key headers only | View raw

MitchAlsup <user5857@newsgrouper.org.invalid> writes:
> John Ames <commodorejohn@gmail.com> posted:
>> The idea I had last time I dabbled with this stuff was to extend the
>> basic add/subtract instructions with an option to save the carry/borrow
>> value in another GPR, instead - but I never gave any thought to how to
>> represent overflow that way. Hmm.
>
> That is what CARRY does. The Rd register in CARRY supplies a register
> used to carry the additional values from calculation to calculation.
> The Immediate in CARRY selects which instruction consume Rd {i},
> which instructions generate the next Rd {o} and which do both {io}
> and which do neither {}.

This is on your 66000?

Kragen

Thread

adding overflow and carry to every GPR (was Re: OT: Epic RISC-V rant) Kragen Javier Sitaker <kragen@canonical.org> - 2026-09-01 17:15 -0300
  Re: adding overflow and carry to every GPR (was Re: OT: Epic RISC-V rant) John Ames <commodorejohn@gmail.com> - 2026-09-01 14:31 -0700
    Re: adding overflow and carry to every GPR (was Re: OT: Epic RISC-V rant) BGB <cr88192@gmail.com> - 2026-09-01 17:18 -0500
    Re: adding overflow and carry to every GPR (was Re: OT: Epic RISC-V rant) MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-09-02 02:04 +0000
      Re: adding overflow and carry to every GPR (was Re: OT: Epic RISC-V rant) John Ames <commodorejohn@gmail.com> - 2026-09-02 08:23 -0700
        Re: adding overflow and carry to every GPR (was Re: OT: Epic RISC-V rant) Kragen Javier Sitaker <kragen@canonical.org> - 2026-09-11 13:48 -0300
          Re: adding overflow and carry to every GPR (was Re: OT: Epic RISC-V rant) MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-09-11 18:03 +0000
      Re: adding overflow and carry to every GPR (was Re: OT: Epic RISC-V rant) Kragen Javier Sitaker <kragen@canonical.org> - 2026-09-02 13:52 -0300
        Re: adding overflow and carry to every GPR (was Re: OT: Epic RISC-V rant) MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-09-02 17:41 +0000
    Re: adding overflow and carry to every GPR (was Re: OT: Epic RISC-V rant) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-09-09 11:16 +0000
  Re: adding overflow and carry to every GPR (was Re: OT: Epic RISC-V rant) MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-09-02 01:53 +0000
  Re: adding overflow and carry to every GPR (was Re: OT: Epic RISC-V rant) EricP <ThatWouldBeTelling@thevillage.com> - 2026-09-05 12:08 -0400
    Re: adding overflow and carry to every GPR (was Re: OT: Epic RISC-V rant) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-09-09 13:36 +0000
  Re: adding overflow and carry to every GPR (was Re: OT: Epic RISC-V rant) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-09-09 10:50 +0000
    Re: adding overflow and carry to every GPR (was Re: OT: Epic RISC-V rant) Paul Rubin <no.email@nospam.invalid> - 2026-09-09 22:10 -0700
    Re: adding overflow and carry to every GPR (was Re: OT: Epic RISC-V rant) Kragen Javier Sitaker <kragen@canonical.org> - 2026-09-11 14:28 -0300

csiph-web