While working on mul_u64_u64_div_u64() improvements I realized that there
is a better way to perform a 64x64->128 bits multiplication with overflow
handling.

Change from v3:

- Added timings to commit log of patch #4.

Link to v3: https://lore.kernel.org/lkml/20240708012749.2098373-2-nico@fluxnic.net/T/

Change from v2:

- Fix last minute edit screw-up (missing one function return type).

Link to v2: https://lore.kernel.org/lkml/20240707171919.1951895-1-nico@fluxnic.net/

Changes from v1:

- Formalize condition for when overflow handling can be skipped.
- Make this condition apply only if it can be determined at compile time
  (guard against the compiler not always inling code).
- Keep the ARM assembly but apply the above changes to it as well.
- Force __always_inline when optimizing for performance.
- Augment test_div64.c with important edge cases.

Link to v1: https://lore.kernel.org/lkml/20240705022334.1378363-1-nico@fluxnic.net/

The diffstat is:

 arch/arm/include/asm/div64.h |  13 +++-
 include/asm-generic/div64.h  | 121 ++++++++++++-----------------------
 lib/math/test_div64.c        |  85 +++++++++++++++++++++++-
 3 files changed, 134 insertions(+), 85 deletions(-)

On Thu, Oct 3, 2024, at 21:16, Nicolas Pitre wrote:
> While working on mul_u64_u64_div_u64() improvements I realized that there
> is a better way to perform a 64x64->128 bits multiplication with overflow
> handling.
>
> Change from v3:
>
> - Added timings to commit log of patch #4.
>
> Link to v3: 
> https://lore.kernel.org/lkml/20240708012749.2098373-2-nico@fluxnic.net/T/

Looks good to me. There are no other comments, I would apply this
in the asm-generic tree for 6.13.

       Arnd

On Fri, 4 Oct 2024, Arnd Bergmann wrote:

> On Thu, Oct 3, 2024, at 21:16, Nicolas Pitre wrote:
> > While working on mul_u64_u64_div_u64() improvements I realized that there
> > is a better way to perform a 64x64->128 bits multiplication with overflow
> > handling.
> >
> > Change from v3:
> >
> > - Added timings to commit log of patch #4.
> >
> > Link to v3: 
> > https://lore.kernel.org/lkml/20240708012749.2098373-2-nico@fluxnic.net/T/
> 
> Looks good to me. There are no other comments, I would apply this
> in the asm-generic tree for 6.13.

Hello Arnd, still no sign of those patches in the asm-generic tree nor 
the linux-next tree.


Nicolas

On Sat, Oct 26, 2024, at 00:36, Nicolas Pitre wrote:
> On Fri, 4 Oct 2024, Arnd Bergmann wrote:
>
>> On Thu, Oct 3, 2024, at 21:16, Nicolas Pitre wrote:
>> > While working on mul_u64_u64_div_u64() improvements I realized that there
>> > is a better way to perform a 64x64->128 bits multiplication with overflow
>> > handling.
>> >
>> > Change from v3:
>> >
>> > - Added timings to commit log of patch #4.
>> >
>> > Link to v3: 
>> > https://lore.kernel.org/lkml/20240708012749.2098373-2-nico@fluxnic.net/T/
>> 
>> Looks good to me. There are no other comments, I would apply this
>> in the asm-generic tree for 6.13.
>
> Hello Arnd, still no sign of those patches in the asm-generic tree nor 
> the linux-next tree.

Thanks for the reminder, I've applied it now.

     Arnd