linux-kernel - Re: [PATCH V3 13/26] csky: Library functions

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Date:   Thu, 6 Sep 2018 16:24:59 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Guo Ren <ren_guo@...ky.com>
Cc:     linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Jason Cooper <jason@...edaemon.net>,
        c-sky_gcc_upstream@...ky.com, gnu-csky@...tor.com,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        wbx@...ibc-ng.org, Greentime Hu <green.hu@...il.com>
Subject: Re: [PATCH V3 13/26] csky: Library functions

On Wed, Sep 5, 2018 at 2:08 PM Guo Ren <ren_guo@...ky.com> wrote:

> --- /dev/null
> +++ b/arch/csky/abiv1/memset.c
> @@ -0,0 +1,38 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (C) 2018 Hangzhou C-SKY Microsystems co.,ltd.
> +#include <linux/types.h>
> +
> +void *memset(void *dest, int c, size_t l)
> +{
> +       char *d = dest;
> +       int ch = c;
> +       int tmp;
> +
> +       if ((long)d & 0x3)
> +               while (l--) *d++ = ch;
> +       else {
> +               ch &= 0xff;
> +               tmp = (ch | ch << 8 | ch << 16 | ch << 24);
> +
> +               while (l >= 16) {
> +                       *(((long *)d)) = tmp;
> +                       *(((long *)d)+1) = tmp;
> +                       *(((long *)d)+2) = tmp;
> +                       *(((long *)d)+3) = tmp;
> +                       l -= 16;
> +                       d += 16;
> +               }
> +
> +               while (l > 3) {
> +                       *(((long *)d)) = tmp;
> +                       d = d + 4;
> +                       l -= 4;
> +               }
> +
> +               while (l) {
> +                       *d++ = ch;
> +                       l--;
> +               }
> +       }
> +       return dest;
> +}

I see that we have a trivial memset() implementation in lib/string.c, but yours
seems to be better optimized. Where did you get it from? Is this a version
that works particularly well on C-Sky, or is this a generic optimized memset
that others could use as well? In the latter case, we could add it to
lib/string.c and let architectures select it in place of the triivial version.

       Arnd