On Thu, Apr 2, 2026 at 2:59 AM Lénárd Szolnoki via Std-Proposals <
std-proposals_at_[hidden]> wrote:

>
>
> On 2 April 2026 06:14:10 BST, Jan Schultke via Std-Proposals <
> std-proposals_at_[hidden]> wrote:
> >While the idea is is worth pursuing, extensible math functions would be a
> >lot of design work that cuts horizontally across several proposals:
> >
> > - P3935R0 "Rebasing <cmath> on C23" adds many more mathematical
> > functions.
> > - P3045R7 "Quantities and units library" also mentions mathematical
> > functions that operate on quantities.
> > - I forgot the number ... we had a proposal that lets you explicitly
> > specify rounding modes for math functions I believe.
> >
> >I suspect that if we were to add quantities and units to the standard
> >library, then new mathematical functions will be part of that library in
> >some way. Being able to std::floor a second or meter or something is a
> >major motivating use case. You should get in touch with the authors and
> see
> >how much overlap there is.
>
> The last thing I want is a single argument std::floor that silently
> returns semantically different quantities when called with meters or
> centimeters.
>
> I'm fine with pow and sqrt (which is a special case), but not a lot of
> other math functions are viable outside of dimensionless quantities.
>

This is exactly right, and thank you for recognizing and articulating this
critical principle.

In the Au units library, we have "floor_as(units, q)" (returning a
quantity) and "floor_in(units, q)" (returning a raw number). You must
always name the unit at the callsite. See the docs
<https://aurora-opensource.github.io/au/main/reference/math/#floor> for
more details.

I assumed mp-units did the same, because they are usually excellent about
unit safety. However, I was alarmed to find that they somehow seem to be
back to a single-argument version
<https://github.com/mpusz/mp-units/blob/master/src/core/include/mp-units/math.h#L335-L349>.
I reopened the issue
<https://github.com/mpusz/mp-units/issues/432#issuecomment-4189300262>, and
I hope it gets resolved promptly.


>
> >
> >On Wed, 1 Apr 2026 at 23:19, Stéphane Gros-Lemesre via Std-Proposals <
> >std-proposals_at_[hidden]> wrote:
> >
> >> Hello,
> >> It is my first time posting here, I'm not sure I am following the proper
> >> process. Please let me know if I'm doing this wrong.
> >>
> >> I wanted to float here this idea, see if there would be interest.
> >> The idea is providing an extension mechanism for std math functions.
> >>
> >> The idea is presented here:
> >> https://github.com/StephaneGrosLemesre/ExtensibleMath
> >>
> >> Or in the attached pdf.
> >>
> >> Please let me know what you think,
> >> Kind regards,
> >> Stéphane
> >> --
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> >>
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