Module reach 

__gunnar_reach__ — reachability bitmaps.

For each selected commit, the set of objects reachable from it — the commit itself, its ancestors, and every tree and blob those commits point at — recorded as a roaring bitmap over object ordinals.

The ordinal space is the archive’s oid-lexicographic ordering of its distinct objects, which is also the order the sorted lookup sub-index is in and the order __gunnar_oid__ records in its ordinal column. So a bitmap position is resolvable to an object with the oid index alone.

What it buys: want − have becomes reach(want) ANDNOT reach(have) — a bitmap operation instead of a graph traversal. No speedup is claimed here. Nothing in this repository has measured it against a real repository with real merge history; the structure is built and correct, the number is not earned (LAW 7).

Cost, stated plainly: the builder is O(commits × bitmap width) in time and holds live bitmaps for commits whose children are not yet processed, plus one memoized tree-closure bitmap per distinct tree. On a wide DAG that is not cheap. ReachPolicy::max_commits bounds how many bitmaps are kept, not how many are computed.

Structs

ObjectFacts

What the builder needs to know about every object in the archive.

ReachEntry

One sealed bitmap.

ReachPolicy

Which commits get a bitmap.

Functions

build_reach

Build the reachability bitmaps.

build_reach_batch

decode_reach

needs_payload

Which objects a repack must hold to make the reachability pass exact.

reach_schema

read_reach

Read the reachability bitmaps out of a sealed archive. Ok(None) when absent.