From: Markus Wichmann <nullplan@gmx.net>
To: musl@lists.openwall.com
Subject: Re: [musl] [PATCH v2 2/2] Use modulo instead of mul+sub in __secs_to_tm
Date: Mon, 1 Mar 2021 20:26:46 +0100 [thread overview]
Message-ID: <20210301192646.GA2766@voyager> (raw)
In-Reply-To: <CAOUYtQCiOiM69sq1QWsNEGMspedGFY7_VBYxef9-hXENeTCnKQ@mail.gmail.com>
On Sun, Feb 28, 2021 at 07:58:27PM +0000, Jon Chesterfield wrote:
> Note that module coming for free with division doesn't make it cheap.
> Integer division is far more expensive that integer multiply on ~ every
> architecture. Several architectures implement division in software. It's
> not cheap on x86, despite the dedicated instruction.
>
> Cheers
And then there's PowerPC, which does have a divide instruction but no
modulo. The manual explicitly states that if you need a modulo, you are
supposed to divide, multiply, and subtract.
Ciao,
Markus
next prev parent reply other threads:[~2021-03-01 19:27 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-28 15:09 [musl] [PATCH] Remove unnecessary if " Mattias Andrée
2021-02-28 17:06 ` Rich Felker
2021-02-28 17:24 ` Mattias Andrée
2021-02-28 17:34 ` Rich Felker
2021-02-28 19:22 ` [musl] [PATCH v2 1/2] " Mattias Andrée
2021-02-28 19:22 ` [musl] [PATCH v2 2/2] Use modulo instead of mul+sub " Mattias Andrée
2021-02-28 19:37 ` Szabolcs Nagy
2021-02-28 19:52 ` Mattias Andrée
2021-02-28 19:58 ` Jon Chesterfield
2021-03-01 19:26 ` Markus Wichmann [this message]
2021-02-28 19:27 ` [musl] [PATCH v3 1/2] Remove unnecessary if " Mattias Andrée
2021-02-28 19:27 ` [musl] [PATCH v3 2/2] Use modulo instead of mul+sub " Mattias Andrée
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