Need to be able to control the level of SIMD through cmake options

[yurivict]

When the package is built it should be built for the lowest common SIMD level supported everywhere, even though the build server might support a higher level. Individual users might want to build individually for their own hardware.

The project should have configuration options to choose the level of SIMD.

Ideally, there should be boolean options:

• SIMD_NONE
• SIMD_NATIVE
• SIMD_SSE2
• SIMD_SSE41
• SIMD_SSE42
  etc, etc.

Otherwise the package built on a server with high SIMD level would crash on an older CPU with lower SIMD support.

[1480c1]

I think it would also be good to have a dispatcher so that a higher simd level does not get called on systems without it, so it would be okay to copy a binary between two different machines

[adamjw24]

The decoder detects the highest available SIMD extension it can use during runtime. So differences between build and runtime machines should not be a problem.

Did you have a specific problem with that? Could you specify more detail about the exact used build/runtime computers?

For testing purposes, it is still possible to restrict SIMD in the code by setting cVVDecParameter.m_eSIMD_Extension in vvdecapp.cpp (there is not cmd parameter because this is not your everyday usecase).

[yurivict]

1. Here https://github.com/fraunhoferhhi/vvdec/blob/master/source/Lib/vvdec/CMakeLists.txt#L72 SSE-4.1/SSE-4.2 are enabled which aren't generally available.

2. Build on powerpc64 failed because of unconditional SSE options. Normally SIMD options should be used only on architectures where they are supported, and generic code should be used elsewhere.

[adamjw24]

As it says in the README.md, VVdeC is a x86 VVC decoder. So if you are compiling on a powerpc64, you should use a cross-compiler with x86 target architecture, in which case the compiler should support the options.

But I guess, since the codebase actually supports it, we might adapt the build process appropriately. This will never be non-experimental and properly tested, though, and low-priority for now.