Missing support for Linux on aarch64

[hesiod]

While packaging geogram for nixpkgs (see relevant PR), we noticed that Geogram is missing proper detection for Linux on aarch64 (even though Darwin on aarch64 and Linux on 32-bit ARM are supported). Geogram would probably compile fine on aarch64, but currently the atomics header assumes it is compiled for x86 when compiling on aarch64 (GEO_USE_X86_ATOMICS is set), resulting in compile errors (see log output).

[BrunoLevy]

It will require a bit of work (the other architectures requires some assembly), but I can try with std::atomic (but I'm a bit unsure of performance. I'll test that, and if it works it will remove a lot of #ifdefs.

[BrunoLevy]

• [x] alternative version of spinlocks using std::atomic, see this link
• [x] compare speed with existing implementation (based on intrinsics and some ASM code)

[kevinbentley]

Any update on this issue? I'd love to be able to use geogram on a project I'm using. I'm no ARM assembly expert, but I think I can port the arm32 code in atomic.h to aarch64 assembly and add some ifdefs, but I don't want to go down that road if there's a better way. I'm willing to put in the work on this, but I have a lot to learn about the internals of geogram. Any advice/direction you could give me is appreciated!

[BrunoLevy]

Hi Kevin, I'd recommend to try using std::atomics, which probably generates assembly as good as one can do manually. I did not have the time to test, but I plan to remove most of these #ifdefs and replace them with portable C++. But I need to measure the impact of performance, which will require some time to do it seriously, and this is why I did not do it before (I am now on a project with more priority on mesh intersection, I plan to do that, but I cannot tell exactly when)

[BrunoLevy]

Since it is based on std::atomic, v1.8.8 should work with aarch64