Better handling of precomputed tables
fjarri opened this issue · 1 comments
We have some precomputed reciprocals that we use in sieving (see precomputed.rs
). We currently use lazy_static
to handle lazy evaluation ofthose.
lazy_static
has some side effects (spin_no_std
feature is enabled for all other instances of lazy_static
in the dependency tree - see rust-lang-nursery/lazy-static.rs#204).
once_cell
is an alternative to it. It will be eventually included in the language (rust-lang/rust#74465). There is a problem though: in order to have no_std
, once_cell
needs the critical-section
feature enabled; critical-section
crate is brittle (it requires the user of the final application to be aware of it and follow some rules; see https://docs.rs/critical-section/latest/critical_section/#usage-in-libraries).
Another variant is, of course, creating the Reciprocal
objects directly during compilation. It doesn't seem to be very slow, but will take about 400kb.
Ideally, whatever we choose, it should be gated by a feature. Need to also test how slow it actually is (especially relatively to the primality checks) to compute the reciprocals on the fly.