BlockSection::get and set check the section index and the state id once,
then read and write through new PackedStorage::read/write, which skip the
storage-level bounds and value checks and the Result that get/set keep for
external callers. A section index is below 4,096 and a palette id always
fits the width bits_for_palette chose; both methods debug_assert that
contract. Used for the hot read, the hot write and the growth re-encode.
Benchmark (ignored tests, best of alternating-order rounds, fast profile):
BlockSection::set 13.15 -> 9.12 ns/write (1.44x), get 2.33 -> 1.45 ns/read
(1.61x). See docs/performance/paletted-container-access-results.md.
BlockSection::set resolved the old cell through get and then probed the
section palette three times per non-trivial write: keying the old state by
id, testing the incoming state and finding it. The slot at the written index
already is the old state's id, so read it straight from storage and resolve
only the incoming state, with a single map probe. Palette reuse, free slots
and growth are unchanged, so palette, counts, free list and NBT are identical.
PalettedContainer::unpack and unpack_u16 matched the palette variant inside
the per-cell loop; dispatch Single/List/Global once before it.
Measured against copies of the pre-optimization code (ignored tests):
BlockSection::set 12.73 -> 11.37 ns/write (1.12x), unpack list 1.956 ->
1.860 us/call (1.05x), global 2.255 -> 2.172 (1.04x). See
docs/performance/paletted-container-access-results.md.
set_matches_baseline_under_random_edits drives both implementations over the
same 50k-edit streams for 1/2/16/17/24/64 distinct states, with periodic
whole-section collapses, and asserts equal results, bits, palette, counts,
free list and NBT.
rdbtCVS