linux-kernel - Re: [PATCH v2] ctype.h: remove duplicate isdigit() helper

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Message-ID: <CANiq72n72FMnNnWveSZOj_3_beXKX03CVL8=cQqqa8QyK-PKig@mail.gmail.com>
Date:   Tue, 27 Oct 2020 10:47:39 +0100
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH v2] ctype.h: remove duplicate isdigit() helper

On Tue, Oct 27, 2020 at 12:57 AM Arnd Bergmann <arnd@...nel.org> wrote:
>
> +#ifdef __has_builtin
> +#define has_builtin(x) __has_builtin(x)
> +#else
> +#define has_builtin(x) (0)
> +#endif

Could this be

    #ifndef __has_builtin
    # define __has_builtin(x) 0
    #endif

? i.e. mimicking what we do for `__has_attribute`.

It would also be a nice idea to put a reminder comment like:

    /*
     * __has_builtin is supported on gcc >= 10, clang >= 3 and icc >= 21.
     * In the meantime, to support gcc < 10, we implement __has_builtin
     * by hand.
     */

Cheers,
Miguel