BitmapView

A serialized bitmap, read where it lies.

Nothing is deserialized. open validates the structure in one pass and keeps only the mapping, the container count and the cardinality; a contains afterwards is a binary search of u16 reads against the file, and a rank is that plus one search inside one block. This is the reason the bitmap format is rabosh's own rather than a library's: an index sidecar is consulted far more often than it is written, and a bitmap that had to be parsed into heap objects first would pay for the whole file to answer a question about one value.

val view = BitmapView.open(segment, offset = handle.offset, length = handle.length, file = name)
view.contains(ordinal)
view.and(other)            // materialises one 8 KB block at a time, never the whole bitmap

A view must not outlive the arena that mapped its segment. It holds no reference the runtime can see, so reading one after its arena has closed is a fault rather than a stale answer — the same rule Variant over a mapped segment follows, and the reason a Snapshot in the storage core is AutoCloseable.

What open checks and what it does not. It checks everything that decides where a byte is: the version, the container count, ascending keys, increasing prefix cardinalities, known container kinds, and that the blocks tile the slice exactly — offsets contiguous from the end of the directory to the last byte. What it does not do is walk the values. Confirming that a bitset's population count matches the cardinality the directory declares would mean reading 1024 words per block on a path whose whole point is to read one, and a bitmap always arrives inside a frame that has already been checksummed — phase 7's sidecar does for a bitmap what SegmentBytes.verifyBlock does for a segment's data block. verify is the deep pass, for tests and for anything that wants to audit a file it did not write.