The narrowing walked each layer twice -- once for _layer_head to read its
name, once to decode it -- which is free when there is a lot to skip and a
straight loss when there isn't. Measured against a cache spanning zooms
2-14: low-zoom tiles carry no buildings, housenumbers or POIs at all
(a z10 tile is 98% drawn layers, a z2 tile 100%), so the whitelist saved
them nothing while the extra walk cost 16-18%.
The name is field 1 and in practice the first thing written, so the walk
already knows by then whether the rest is worth keeping; from there an
unwanted layer is stepped over rather than copied out. Field order isn't
guaranteed though, so the flag is only an optimisation -- the decision is
the check after the loop, which is right however the fields arrived and
also covers a layer declaring no name at all. _layer_head goes away.
On the regular platform this turns a 0.97x into a 1.03x on low-zoom
tiles and 1.00x on the largest, while urban z14 tiles keep their 3.19x;
the whole 293-tile cache goes 1.4x -> 1.6x. On the Lyra the median tile
is 3.24x and the largest 4.85x, both up.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Jean-Pierre MartineauandClaude Opus 5
71e979eadb