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

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Date:   Thu, 6 Sep 2018 17:50:02 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Guo Ren <ren_guo@...ky.com>,
        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 Thu, Sep 6, 2018 at 4:25 PM Arnd Bergmann <arnd@...db.de> wrote:
> 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;

while ((uintptr_t)d & 0x3) && l--)
        *d++ =ch;

and remove the else below?

> > +       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;

s/long/u32/

> > +                       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.

Sounds good to me, after removing the 32-bit-isms.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds