BigPrimeNumber.cpp

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#include "./Abs.h"
#include "./extrema.h"
 
namespace bamg {
 
   long BigPrimeNumber(long n){
      /*Original code from Frederic Hecht <hecht@ann.jussieu.fr> (BAMG v1.01, Mesh2.cpp/AGoodNumberPrimeWith)*/
 
      /*list of big prime numbers*/
      const long BigPrimeNumber[] ={ 567890359L,
         567890431L,  567890437L,  567890461L,  567890471L,
         567890483L,  567890489L,  567890497L,  567890507L,
         567890591L,  567890599L,  567890621L,  567890629L , 0};
 
      /*initialize o and pi*/
      long o  = 0;
      long pi = BigPrimeNumber[1];
 
      /*loop until BigPrimeNumber[i]==0 (end of BigPrimeNumber)*/
      for (int i=0; BigPrimeNumber[i]; i++){
 
         /*compute r, remainder of the division of BigPrimeNumber[i] by n*/
         long r = BigPrimeNumber[i] % n;
 
         /*compute oo = min ( r , n-r , |n - 2r|, |n-3r|)*/
         long oo = Min(Min(r,n-r),Min(Abs(n-2*r),Abs(n-3*r)));
         if(o < oo){
            o  = oo;
            pi = BigPrimeNumber[i];
         }
      }
      return pi; 
   }
}