@Sourabh m=2^s***d primes[i]*<*n
On 2012-1-18 19:39, Sourabh Singh wrote:
@Terrence sry i didn't explain what s,d were they were also wrong i ws calculating for n not n-1 earlier n=2^s+d nw m=n-1; for odd n m=2^s+d; //suggested corrections made.. still not working.. #include<iostream> #include<conio.h> #include<math.h> using namespace std; int is_prime(int n) { if(n==2 | n==3) return 1; if(((n-1)%6!=0& (n+1)%6!=0) || n<2) return 0; int m=n-1; int s,d; for(s=0;1<<s<m;++s); s--;d=(m%(1<<s)); int primes[6]={2,3,7,31,61,73},i,a,flag; uint64_t x; for(i=0;i<6;i++) { if(primes[i]>n) break; a=primes[i]; x=uint64_t(pow(a,d))%n; if(x==1 || x==n-1) continue; for(int r=1;r<s;r++) { x=(x*x)%n; if(x==1) return 0; if(x==n-1) break; } if(x!=n-1) return 0; } return 1; } main() {for(int k=1;k<20;k++) printf("%d is %d\n",k,is_prime(k)); getch();} On 1/18/12, Sourabh Singh<singhsourab...@gmail.com> wrote:@ sunny agrawal you are right. but i have used check a>n also . no improvement . i think algo is wrong in later part.. somewhere.. @ Terence 1) pow may not work for big n but , m just checking for n=1..200 just to check wether algo is right.. and it's not working even for n=7,19... 2) d,s are also coming fine for small values.. of n 3) for x i have used... 64bit integer.. uint64_t in it's declaration. i just want to get algo right first then bother about big n ;-) On 1/18/12, Terence<technic....@gmail.com> wrote:1. the computing of d is incorrect. d = n-1; while((d&1)==0) d>>=1; 2. the accuracy of pow is far from enough. you should implement your own pow-modulo-n method. 3. for big n, (exceed 32bit), x=(x*x)%n can be overflow also. you may need to implement your own multiply method in this case. On 2012-1-18 18:15, Sourabh Singh wrote:@all output's to above code are just random.. some prime's. found correctly while some are not why i used certain primes to check ie.(2,3,31,73,61,7) coz.. its given n wiki for about 10^15 checking with these is enough.. On 1/18/12, Sourabh Singh<singhsourab...@gmail.com> wrote:@ALL hi everyone m trying to make prime checker based on miller-rabin test . can some1 point out . wat's wrong with the code. thank's alot in advance... //prime checker based on miller-rabin test #include<iostream> #include<conio.h> #include<math.h> int is_prime(int n) { if(n==2 | n==3) return 1; if(((n-1)%6!=0& (n+1)%6!=0) || n<2) return 0; int s,d; for(s=0;1<<s<n;++s); s--;d=(n%(1<<s)); int primes[6]={2,3,7,31,61,73},i,a,flag; uint64_t x; for(i=0;i<6;i++) { flag=0; a=primes[i]; x=uint64_t(pow(a,d))%n; if(x==1 | x==n-1) continue; for(int r=1;r<s;r++) { x=(x*x)%n; printf("x is %llu\n",x); if(x==1) return 0; else flag=1; } if(flag) continue; return 0; } return 1; } main() { for(int k=1;k<100;k++) { printf("%d is %d\n",k,is_prime(k)); } getch(); } -- You received this message because you are subscribed to the Google Groups "Algorithm Geeks" group. To post to this group, send email to algogeeks@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.-- You received this message because you are subscribed to the Google Groups "Algorithm Geeks" group. To post to this group, send email to algogeeks@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.
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