A coordinate read cost 0.082 ms in a 500-record store and 0.081 ms in a 20,000-record
one — flat to a microsecond while the index search does nine probe reads against
fifteen. So the device reads are nearly free and the per-call cost is SETUP, and the
clearest piece of setup was a copy of the log window into a second buffer on every read.
`v3_get` copied it because what the log says borrows it while reading the image needs
`&mut image`; that borrow is one field, so moving the field out settles it for nothing.
Measured on #82: get 0.082 -> 0.078 ms, spaces 0.339 -> 0.267 ms. That is small in the
GUEST, and the guest cannot show the real number: its store carries a log of a few
hundred bytes, while the box's log is 132,679 bytes — so the copy this removes costs
~130 KB of memcpy and a ~130 KB allocation per read there, and only the box can measure
it.
Also names the store's own class bit. `BOOT_FLAGS` was a bare `1 << 7` and read as
`TYPE_MASK == 10` ("data type: code") to anything applying `WordFlags` — a latent
collision, not a live one, and the resolution is a declaration rather than a move:
`WordFlags` is a different field and its sixteen bits are all allocated, so there is no
bit to borrow, and the space axis already makes a boot record findable (reserved space
0xFC) without a class bit at all. What it needed was a vocabulary that claims it, which
this comment now does. The one bit the two fields share is shared on purpose and by name:
0x0800, `SEALED_FLAG` in `cube-store-seal`, which `WordFlags` calls `ENCRYPTED` — same
meaning in both places, which is the pattern rather than the exception.
surface-camera-build
aab316a9a1