Backend Selection

Rsassy installs a C shim plus Rust backend libraries. One backend is selected per R process.

Auto selection

backend = "auto" uses the first installed and supported backend in this order:

  1. wasm_simd128
  2. avx512
  3. avx2
  4. neon
  5. scalar
sassy_features()
#> <sassy_features>
#> dispatch: dynamic
#> selected backend: avx2
#> installed backends: scalar, avx2, avx512
#> supported backends: scalar, avx2
#> CPU: avx2=yes avx512f=no neon=no
#> Rust backend: avx2 (native_simd=yes)

Explicit selection

Call sassy_set_backend() before any other Rsassy native call. Backend loading is one-shot, so test another backend in a new R process.

script <- tempfile(fileext = ".R")
writeLines(c(
  "library(Rsassy)",
  "sassy_set_backend('scalar')",
  "print(sassy_features())"
), script)
cat(system2(file.path(R.home("bin"), "Rscript"), c("--vanilla", script), stdout = TRUE), sep = "\n")
#> <sassy_features>
#> dispatch: dynamic
#> selected backend: scalar
#> installed backends: scalar, avx2, avx512
#> supported backends: scalar, avx2
#> CPU: avx2=yes avx512f=no neon=no
#> Rust backend: portable_scalar (native_simd=no)
unlink(script)

Why separate backend libraries?

The sassy crate uses build-time SIMD configuration and SIMD-dependent types. The R package therefore builds separate Rust libraries for the supported backend families instead of switching individual functions at runtime.