Large Memory Consumption on Region Covering

[KarlRunge]

While trying to cover a region of lat lon (Lat: -37 -> -38, Lon: 147 -> 148), While getting all the CellIds in that region. The function call seems to use approx 2.5gb of RAM, which what should be approx 200mb.

Reproduction code:

let coverer = s2::region::RegionCoverer {
    min_level: 19,
    max_level: 19,
    level_mod: 0,
    max_cells: usize::MAX,
};

let rect = s2::rect::Rect::from_degrees(
    -38.0,
    144.0,
    -37.0,
    145.0,
);
let children_cells = coverer.covering(&rect).0;

[yjh0502]

I tried to reproduce the result by myself. Here's code snippet that I used to reproduce: https://gist.github.com/yjh0502/377ea1998e74abcd40a38bf7e4eab73a

• # of cells does not match (probably a bug?), but in similar scale (go 40024944 / rust 40040019)
• wall clock times are comparable (go 0:30.58 / rust 0:22.07) and max RSSs are also in comparable range (go 10285MB / rust 4775MB)

I believe 200mb comes from memory usage to store output ((8b * 40040019) / (2**20) ~= 305mb). It seems covering requires more memory for calculation.