linux-kernel - Re: [PATCH V6 13/33] csky: Library functions

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Message-ID: <20180929170011.GA27796@guoren-Inspiron-7460>
Date:   Sun, 30 Sep 2018 01:00:11 +0800
From:   Guo Ren <ren_guo@...ky.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     akpm@...ux-foundation.org, arnd@...db.de,
        daniel.lezcano@...aro.org, davem@...emloft.net,
        gregkh@...uxfoundation.org, jason@...edaemon.net,
        marc.zyngier@....com, mark.rutland@....com,
        mchehab+samsung@...nel.org, peterz@...radead.org, robh@...nel.org,
        robh+dt@...nel.org, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        devicetree@...r.kernel.org, green.hu@...il.com,
        Chen Linfei <linfei_chen@...ky.com>,
        Mao Han <han_mao@...ky.com>
Subject: Re: [PATCH V6 13/33] csky: Library functions

On Fri, Sep 28, 2018 at 09:20:30AM -0700, Christoph Hellwig wrote:
> > +unsigned long long notrace __bswapdi2(unsigned long long u)
> > +{
> > +	return (((u) & 0xff00000000000000ull) >> 56) |
> > +	       (((u) & 0x00ff000000000000ull) >> 40) |
> > +	       (((u) & 0x0000ff0000000000ull) >> 24) |
> > +	       (((u) & 0x000000ff00000000ull) >>  8) |
> > +	       (((u) & 0x00000000ff000000ull) <<  8) |
> > +	       (((u) & 0x0000000000ff0000ull) << 24) |
> > +	       (((u) & 0x000000000000ff00ull) << 40) |
> > +	       (((u) & 0x00000000000000ffull) << 56);
> > +}
> 
> How is this any better than using the generic byteswap helpers?
OK.
#include <uapi/linux/swab.h>

unsigned long long notrace __bswapdi2(unsigned long long u)
{
	return ___constant_swab64(u);


> 
> > +unsigned int notrace __bswapsi2(unsigned int u)
> > +{
> > +	return (((u) & 0xff000000) >> 24) |
> > +	       (((u) & 0x00ff0000) >>  8) |
> > +	       (((u) & 0x0000ff00) <<  8) |
> > +	       (((u) & 0x000000ff) << 24);
> > +}
> 
> Same here.
OK.
#include <uapi/linux/swab.h>

unsigned int notrace __bswapsi2(unsigned int u)
{
	return ___constant_swab32(u);
}

Thx
 Guo Ren