[bug#61586] BinaryEn

[Liliana Marie Prikler]

Am Samstag, dem 11.03.2023 um 23:48 +0100 schrieb Andreas Enge:
> Hello Liliana,
Hi Andreas, please don't forget to add me in CC.

> how about you start by pushing the python-filecheck package?
I'd only do that if it has another user and for the time being I don't
see that.  Don't worry, I still got more python packages in my backlog
:)

> Do you have a pointer to BinaryEn using -msse2 for precision?
> I am not familiar with SSE2, but a quick look-up on Wikipedia only
> shows (packed) double floating point operations and packed integer
> arithmetic.
> All these should be feasible directly in C, although maybe more
> slowly.
Possible, but more slowly in C doesn't translate that nicely if you
don't want to code up your own float/double types and you really don't
want that.

The problem here is that expressions like:
  double a, b, c;
  c = sqrt(a * a, b * b);
can use 80 bit intermediaries on x87 chips, which they don't when using
SSE2 – hence the precision argument.  You would have to redefine all
basic operations for your floating point (which would still be doable
in C++ due to operator overloading, but be a major pain in the butt to
do correctly and well-tested, hence the deference to SSE2, I believe).

> In the CMakeLists.txt file there are the following lines:
>   if(NOT EMSCRIPTEN)
>     if(CMAKE_SYSTEM_PROCESSOR MATCHES "^i.86$")
>       # wasm doesn't allow for x87 floating point math
>       add_compile_flag("-msse2")
>       add_compile_flag("-mfpmath=sse")
>     elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "^armv[2-6]" AND NOT
> CMAKE_CXX_FLAGS MATCHES "-mfpu=")
>       add_compile_flag("-mfpu=vfpv3")
>     endif()
>   endif()
> 
> So the -msse2 flag will not be added on arm; the package is compiled
> successfully on aarch64, and I see no reason why in principal it
> should not also work on armhf. 
It does require the vfpv3 fpu, which I believe won't exist on all arms.

> Maybe there is a more precise test for x86_64 that could be used
> instead of
>     if(CMAKE_SYSTEM_PROCESSOR MATCHES "^i.86$") ?
Not for the kind of check they want to make, I believe.

Cheers