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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
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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