FluidX3D v2.12 (faster startup)

Thank you for using FluidX3D! Update v2.12 significantly reduces compile and startup time:

• if make is installed, source code compiling on Linux is now ~3x faster using multiple CPU cores, from ~15s to ~5s
• simulation initialization for single-GPU simulations is ~40% faster now
• simulation initialization for multi-GPU simulations is ~15% faster now

Bug fixes:

• minor bug fix in Memory_Container::reset() function

Here is how launch time changed with FluidX3D versions:

Setup: 3D Taylor-Green vortices, single 384³ domain, D3Q19 SRT FP32/FP16S
Hardware: Lenovo Y50-70, i7-4720HQ, 2x 8GB DDR3 1600 MT/s, GTX 960M 4GB

I had compared all previous versions and found v2.0 to introduce a big jump in startup time. This was due to changing LBM data field access from direct array access to domain decomposition indexing, which turned out as the main bottleneck during simulation startup. This is now fixed, with an indexing shortcut for single-GPU and pre-computing variables for multi-GPU indexing. Together with multi-core parallelization of initialization (v2.9) and faster buffer initialization (v2.11), launch time is now shorter than ever.

Have fun with the software!
-- Moritz