stage1 HashMap: store hash & do robin hood hashing #5779
Merged
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
This adds these two fields to a HashMap Entry:
uint32_t hash
uint32_t distance_from_start_index
Compared to master branch, standard library tests compiled 8.4% faster
and took negligible (0.001%) more memory to complete. The amount of
memory used is still down from before 8b82c40 which moved indexes
to be stored separately from entries.
So, it turns out, keeping robin hood hashing plus separating indexes
did result in a performance improvement. What happened previously is
that the gains from separating indexes balanced out the losses from
removing robin hood hashing, resulting in a wash.
This also serves as an inspiration for adding a benchmark to
std.AutoHashMap and improving the implementation.