It is sometimes useful to remove all elements of a bitset while retaining the
backing storage. With a dense bitset, we would just memset everything to 0,
which is O(capacity). With a sparse bitset, previously we would have to free and
reallocate, which is O(capacity) in the dense case and O(cardinality) in the
sparse case. That is the correct asymptoptic behaviour O(cardinality) in the
worst case, but there is an unfortunate constant-factor associated with the
redundant allocation & free in the dense case.
Therefore, we add a new helper to clear all elements of the sparse bitset in one
go, avoiding reallocation in the dense case.
Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@intel.com>
Reviewed-by: Natalie Vock <natalie.vock@gmx.de>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/40806>
Useful for potentially huge bitsets that are expected to be mostly
filled with zeroes, reducing memory consumption by assuming bits being
zero by default (without wasting memory to store zeroes).
Co-authored-by: Alyssa Rosenzweig <alyssa.rosenzweig@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37908>
