fix(web): a sky's marks spread all the way round each cluster (refs #157) eb56c8bc4d0e

/// FNV-1a, then splitmix64's finaliser: a small, stable hash, so a

/// repository's place never changes. The finaliser spreads every bit:

/// FNV alone gives names that differ only at the end (`repo#1`, `repo#2`)

/// alike high bits, which drew a cluster's marks as fans at a few angles.

    h = (h ^ (h >> 30)).wrapping_mul(0xbf58_476d_1ce4_e5b9);

    h = (h ^ (h >> 27)).wrapping_mul(0x94d0_49bb_1331_11eb);

    h ^ (h >> 31)

    fn a_clusters_marks_spread_all_the_way_round() {

        let repos = vec![Repo { name: "doomsdayone/rstar-api".into() }];

        let events: Vec<Event> = (0..200).map(|_| Event { repo: 0, kind: Kind::Issue, age_days: 1.0, n: 1 }).collect();

        let s = Sky::new(&repos, &events, 1600.0, 900.0, true);

        // Every eighth of the circle holds a fair share of the marks.

        let mut octants = [0u32; 8];

        for m in s.marks.iter().filter(|m| m.kind == Kind::Issue) {

            octants[((m.angle / TAU * 8.0) as usize).min(7)] += 1;

        }

        assert!(octants.iter().all(|&n| (12..=40).contains(&n)), "{octants:?}");

    }

    #[test]