mirror of https://github.com/CGAL/cgal
46 lines
1.0 KiB
C++
46 lines
1.0 KiB
C++
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#ifndef CGAL_PRIMES_H
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#define CGAL_PRIMES_H
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#include <CGAL/basic.h>
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namespace CGAL {
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namespace CGALi {
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extern int primes[2000];
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static inline
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int get_next_lower_prime(int current_prime){
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bool is_prime = false;
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int i;
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CGAL_precondition_msg(current_prime != 2 ," primes definitely exhausted ");
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if((current_prime <= 7) && (current_prime > 2)){
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if(current_prime <= 5){
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if(current_prime == 3)
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return 2;
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return 3;
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}
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return 5;
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}
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for(i=current_prime-2;(i>1 && !is_prime);i=i-2){
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int r = 1;
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for(int j=3; (j <= i/2 && (r != 0)); j++){
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r = i % j;
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// std::cout<<"i " <<i<<std::endl;
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// std::cout<<"j " <<j<<std::endl;
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// std::cout<<"i%j " <<i%j<<std::endl;
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if(j==i/2 && r != 0)
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is_prime = true;
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}
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}
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// CGAL_precondition_msg(is_prime," primes definitely exhausted ");
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return i+2;
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}
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}
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}
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#endif // CGAL_PRIMES_H
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