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Matthias Kretz | Vir

@mkretz@floss.social

🧔🏻‍♂️👩🏽 👦🏻👧🏻👧🏻, C++ committee numerics chair, std::simd / SIMD specialist, CS PhD, Dipl.-Phys, nuclear physics, former KDE core developer, FLOSS user & supporter, anti fascist, 🏋️‍♂️, 🏊‍♂️🚴‍♂️🏃‍♂️

Profile picture: me on my Aeroad racing in a triathlon

Header picture: @mkretz@floss.social

#SIMD #stdsimd #WG21 #Cpp #GCC #KDE #roadcycling #running #triathlon #Darmstadt #DSW12triathlon

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12 Posts

Joined December 01, 2022

GitHub:

https://github.com/mattkretz

ORCID:

https://orcid.org/0000-0002-0867-243X

Blog:

https://mattkretz.github.io/

Garmin Connect:

https://connect.garmin.com/modern/profile/4827aa7d-deae-410e-82f6-98b73fe8e659

Posts

Matthias Kretz | Vir @mkretz@floss.social · May 08, 2026

@mhoemmen@c.im mdspan feature request 😉:
Allow mdspan::operator[] with one argument less than rank.
Mandates/Constraints: The resulting range is contiguous in memory.
Returns: A span (of static extent, if possible).

Then I can use std::simd CTAD from range:
simd::basic_vec(B[k], simd::flag_aligned);

instead of:
simd::unchecked_load>(&B[k, 0], &B[k, N-1], simd::flag_aligned);

The former is not only simpler but also safer.

#WG21 #cpp29

Matthias Kretz | Vir @mkretz@floss.social · May 07, 2026

I've been looking into matrix multiplication using std::simd and std::mdspan/submdspan (all single-threaded).
I got to 86% of peak FLOP. x86_64 AVX2 has 32/16 FLOP/cycle peak (2 FMAs per cycle).
I suspect better performance needs a more cache-friendly layout mapping. This is using layout_right.

#stdsimd #simd #mdspan #cpp26 #cpp

Matthias Kretz | Vir @mkretz@floss.social · Apr 29, 2026

I wrote a blog post "My vision for an interdisciplinary RSE institute: how to actually help scientists": https://mattkretz.github.io/2026/04/28/vision-rse-institute.html after learning about @futursi@mas.to

I'm happy to learn what others think about the topic!

#RSE

Matthias Kretz | Vir @mkretz@floss.social · Apr 23, 2026

RE: @danielskatz@fediscience.org

🎉 Seems like my #stdsimd work will finally be easier to recognize as research output.

Matthias Kretz | Vir @mkretz@floss.social · Apr 22, 2026

The #GCC16 branch has been created. A #GCC 16.1 release is imminent. I already adjusted my https://github.com/mattkretz/cplusplus-ci GCC CI images accordingly. If it builds, you can then get gcc-17 images, too.

Matthias Kretz | Vir @mkretz@floss.social · Apr 22, 2026

Replying to @JSAMcFarlane@mastodon.ie

@JSAMcFarlane@mastodon.ie I didn't dare!

Matthias Kretz | Vir @mkretz@floss.social · Apr 22, 2026

Replying to @JSAMcFarlane@mastodon.ie

@JSAMcFarlane@mastodon.ie Oh wow, I was not aware of your P0827! I agree on the usefulness of having a UDL for std::cw for even terser syntax. However, the obvious suffix cw is going to be a hard sell because of hex literals. (It just needs an additional w literal and a smart parser that drops the final c 🙈)

Matthias Kretz | Vir @mkretz@floss.social · Apr 22, 2026

I'm a bit sad today. Yesterday I pushed https://forge.sourceware.org/gcc/gcc-mirror/commit/804bde962de4819138951aed24b2c8ba768d7344, which makes a simple `x + 1` ill-formed: https://compiler-explorer.com/z/4rYx87fcW. Now, in generic code, you write `+ std::cw<1>` instead. If you know the value-type (`float` in this case), just use the appropriate literal (if it exists): `x + 1.f`.

#stdsimd #cpp26

Matthias Kretz | Vir @mkretz@floss.social · Mar 28, 2026

On my way back from #WG21 in Croydon/London. #cpp26 is done. Notable change that I got through: You don't have to wonder anymore what difference there is between `constant_arg` and `constant_wrapper`. Only the latter remains. And `constant_wrapper` now works as a function-wrapper, too (passing a callable as constant expression via function argument).
And—somewhat sad—but `simd::vec(...) * 2` won't compile anymore. I'll have to update GCC16 accordingly.

floss.social

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Matthias Kretz | Vir @mkretz@floss.social · Mar 22, 2026

std::simd "Hello World" on Compiler Explorer:
https://compiler-explorer.com/z/nTK4xc96f

#cpp26 #cpp #cplusplus

Matthias Kretz | Vir @mkretz@floss.social · Mar 21, 2026

The first part of std::simd just landed in #GCC 16: https://forge.sourceware.org/gcc/gcc-mirror/commit/8be0893fd98c9a89bbcd81e0ff8ebae60841d062
Expect it on Compiler Explorer in — I guess — 12 hours.

#simd #wg21 #cpp #cpp26 #cplusplus

Matthias Kretz | Vir @mkretz@floss.social · Feb 11, 2026

Replying to @Chris2000SP@social.anoxinon.de

@Chris2000SP @Azarilh @gonun13 Social interaction on the internet is not the problem. Big tech using their (quasi) monopoly to influence user behavior for "shareholder value" is the problem. E.g., there are some good videos on YT; but I hate to go there because it tries to capture as much of my time as possible. Same for any other commercial platform. Most adults can't deal with this properly. Kids on *social* media, fine. Kids on "commercial influencer", "the user is the product" platforms, NO.

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