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Message-ID: <20230601092413.6679c6a6@inria.fr>
Date: Thu, 1 Jun 2023 09:24:13 +0200
From: Jₑₙₛ Gustedt <jens.gustedt@...ia.fr>
To: Alexander Monakov <amonakov@...ras.ru>
Cc: musl@...ts.openwall.com
Subject: Re: [C23 128 bit 4/4] C23: implement proper support for
int128_t and uint128_t
Alexander,
on Wed, 31 May 2023 20:09:29 +0300 (MSK) you (Alexander Monakov
<amonakov@...ras.ru>) wrote:
> On Wed, 31 May 2023, Jens Gustedt wrote:
>
> > So what? On the arch where it exist, it is used and useful. (And I
> > also think that implementations improved over the state from 20
> > years ago that you describe.)
>
> Sorry, I'm not sure what you meant in the parenthetical statement.
> Improved in what sense?
In the sense that depending on your -march=xxx settings they use all
low level operations that are available. IIRC, bit operation support
is e.g already quite good on most current x86_64, there is
specialization for multiplying or dividing a 128 bit integer with/by a
64 bit integer, and when I did these patches I have seen that division
by a small constant is quite good.
The composition of 64 bit operations is still used as a fallback where
no such native processor support is available, though.
Jₑₙₛ
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