Hi Marten,

By default, they won't work at all - Python runtime error will be raised or
segfault/illegal instruction error may occur. However, if Linux distros or
downstream packagers want to change this default setting, they can do it
through the build options, but without manual SIMD support for the baseline
- just the scalar fallbacks. They can still count on the dispatched kernels
for newer processors.

I have also updated the docs providing an example for this case, see:
https://github.com/numpy/numpy/blob/c41541abe9656987c34eb3f5822879ade84ec612/doc/source/reference/simd/build-options.rst#targeting-older-cpus
On Sat, May 17, 2025 at 4:01 PM <m...@astro.utoronto.ca> wrote:

> Hi Sayed,
>
> I'm a bit confused: does your suggested change mean that prre-2009
> processors won't work at all, or that no use will be made of the (little)
> acceleration that they provided?  The latter seems fine, but not working at
> all seems rather bad. Though I'd think that for any old processors one can
> just fall back to the standard `libm` implementations.
>
> All the best,
>
> Marten
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>


--
Cheers,
Sayed

Sayed Adel
GitHub: seiko2plus
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