basic_dsp_vector offers several feature flags which determine how the calculation is performed. All feature flags are still experimental and under investigation, so it's highly recommended to read their description below before activating it.
The next table marks the allowed combinations for feature flags with an X.
| use_sse2 | use_avx2 | use_gpu | no_std | |
|---|---|---|---|---|
| use_sse2 | X | X | X | X |
| use_avx2 | X | X | X | X |
| use_gpu | X | X | X | |
| no_std | X | X | X |
Activate with: --features use_sse2 or --features use_avx2. Requires Rust Nightly.
This enables explicit SSE2 and AVX2 support. SSE2 and AVX2 are vector instructions which are supported by some CPUs (e.g. Intel and AMD) which speed up the calculations. Without any of those feature flags the lib relies on rustc to vectorize the code, and typically rustc does a very good job on that as long as it's called with the correct arguments (-C target-cpu=native -C target-feature=+sse2,+sse3,+avx2,+avx). There are however some cases where explicit vectorization is useful. The feature flags require the stdsimd crate.
Activate with: --features use_gpu.
use_gpu relies on opencl and clFFT to implement some operations (right now fft and convolve_signal) on the GPU. GPUs have the advantage that they allow highly parallel processing which is beneficial for many DSP operations. However GPUs also have the disadvantage that they have a high latency, which means that it takes time to move data to the GPU and back to the host CPU. For a library like basic_dsp_vector with many low level DSP operations, the high latency is a major drawback. Therefore the GPU is only used if the vector length exceeds a predefined threshold.
To run basic_dsp_vector with use_gpu at least one opencl driver must be installed (e.g. one of Intel, NVidia or AMD) and the clFFT library must be in the library path. Users should keep in mind that many consumer GPUs are optimized for f32 operations and will be rather slow on f64 data.
Activate with: --no-default-features.
--no-default-features will disable the std feature flag. basic_dsp_vector will then compile using only Rust core and without any threading. This allows the lib to be used in more restrictive environments, e.g. embedded devices.
Keep in mind that rustfft still depends on std.