Re: [PATCH 01/12] x86_64: memset_user()

Cyrill Gorcunov
2018-12-21T20:05:50Z

On Fri, Dec 21, 2018 at 10:25:16AM -0800, Matthew Wilcox wrote:
> On Fri, Dec 21, 2018 at 08:14:12PM +0200, Igor Stoppa wrote:
> > +unsigned long __memset_user(void __user *addr, int c, unsigned long size)
> > +{
> > + long __d0;
> > + unsigned long pattern = 0;
> > + int i;
> > +
> > + for (i = 0; i < 8; i++)
> > + pattern = (pattern << 8) | (0xFF & c);
>
> That's inefficient.
>
> pattern = (unsigned char)c;
> pattern |= pattern << 8;
> pattern |= pattern << 16;
> pattern |= pattern << 32;

Won't

pattern = 0x0101010101010101 * c;

do the same but faster?