lkml.org 
[lkml]   [2018]   [Jan]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v10 1/3] lib: Add strongly typed 64bit int_sqrt
It has been some time now since this moved. I have decided not to use
David's implementation because I want to maintain also range above
2^62

Are there any additional objections for this not to go in as it is?

On 22 December 2017 at 14:44, Crt Mori <cmo@melexis.com> wrote:
>
> From simple strong typing of existing int_sqrt we came to something a
> bit more complex or better. Can we decide now which we want in, or I
> submit v12 and we decide then (although it is not a v12, but whole new
> thing)?
>
> On 21 December 2017 at 15:48, David Laight <David.Laight@aculab.com> wrote:
> > From: Peter Zijlstra
> >> Sent: 21 December 2017 14:12
> > ...
> >> > > This part above looks like FLS
> >> > It also does the rest of the required shifts.
> >>
> >> Still, fls() + shift is way faster on hardware that has an fls
> >> instruction.
> >>
> >> Writing out that binary search doesn't make sense.
> >
> > If the hardware doesn't have an appropriate fls instruction
> > the soft fls()will be worse.
> >
> > If you used fls() you'd still need quite a bit of code
> > to generate the correct shift and loop count adjustment.
> > Given the cost of the loop iterations the 3 tests are noise.
> > The open coded version is obviously correct...
> >
> > I didn't add the 4th one because the code always does 2 iterations.
> >
> > If you were really worried about performance there are faster
> > algorithms (even doing 2 or 4 bits a time is faster).
> >
> > David
> >

\
 
 \ /
  Last update: 2018-01-14 23:19    [W:0.092 / U:2.296 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site