linux-kernel - Re: [PATCH v4 1/3] math.h: add DIV_ROUND_UP_NO

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Message-ID: <CAHk-=wgs2DDdckcONG+YbB-GDH2QFCoZJ=Vm+YXxb1moZzuDgQ@mail.gmail.com>
Date:   Wed, 25 Oct 2023 07:43:34 -1000
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Vasily Gorbik <gor@...ux.ibm.com>
Cc:     Sebastian Reichel <sebastian.reichel@...labora.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        David Laight <David.Laight@...lab.com>,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        Niklas Schnelle <schnelle@...ux.ibm.com>, kernel@...labora.com
Subject: Re: [PATCH v4 1/3] math.h: add DIV_ROUND_UP_NO_OVERFLOW

On Wed, 25 Oct 2023 at 05:05, Vasily Gorbik <gor@...ux.ibm.com> wrote:
>
> You probably want
>
>  #define __div_round_up(n,d) _Generic((n)+(d),          \
>         unsigned long long: __div_round_up_ull,         \
>         long long: __div_round_up_ll,                   \
>         unsigned long: __div_round_up_ul,               \
>         long: __div_round_up_l,                         \
>         unsigned int: __div_round_up_u,                 \
>         int: __div_round_up_i)(n,d)
>
> to avoid early type-checking for expressions that will be discarded
> and prevent errors like:

Ack. I noticed that later when I tried to do a bigger config build -
the compiler would warn about the implicit truncation of the integer
arguments (for the cases where they weren't used).

> Plus typos fixes below passes allyesconfig for s390, 32-bit x86 and arm.

Lovely.

It would have been even better if somebody told me that I was stupid
and there was some nice trick to it, but at least the _Generic()
approach doesn't seem broken - just a few tweaks needed.

               Linus