On Tue, Oct 08, 2019 at 12:02:07PM +0200, Rasmus Villemoes wrote:
On 08/10/2019 11.31, Daniel Thompson wrote:
quoted
On Mon, Oct 07, 2019 at 08:43:31PM +0200, Rasmus Villemoes wrote:
quoted
On 07/10/2019 17.28, Daniel Thompson wrote:
quoted
On Thu, Sep 19, 2019 at 04:06:18PM +0200, Rasmus Villemoes wrote:
It feels like there is some rationale missing in the description here.
Apart from the function call overhead (and resulting register pressure
etc.), using int_pow is less efficient (for an exponent of 3, it ends up
doing four 64x64 multiplications instead of just two). But feel free to
drop it, I'm not going to pursue it further - it just seemed like a
sensible thing to do while I was optimizing the code anyway.
[At the time I wrote the patch, this was also the only user of int_pow
in the tree, so it also allowed removing int_pow altogether.]
To be honest the change is fine but the patch description doesn't make
sense if the only current purpose of the patch is as a optimization.
Agreed. Do you want me to resend the series with patch 3 updated to read
"For a fixed small exponent of 3, it is more efficient to simply use two
explicit multiplications rather than calling the int_pow() library
function: Aside from the function call overhead, its implementation
using repeated squaring means it ends up doing four 64x64 multiplications."
(and obviously patch 5 dropped)?
Yes, please.
When you resend you can add my R-B: to all patches:
Reviewed-by: Daniel Thompson <redacted>
Daniel.
PS Don't mind either way but I wondered the following is clearer than
the slightly funky multiply-and-assign expression (which isn't wrong
but isn't very common either so my brain won't speed read it):
retval = DIV_ROUND_CLOSEST_ULL(retval * retval * retval,
scale * scale);