gistfile1.cpp

const int MAXN = 110000;
int mask[MAXN];
static int primes[10000]={2,3,5,7,9};
int size = 0;
bool TestPrime(const CBigNum& p){
        for(int i = 0; i < 5; ++i){
                CBigNum remain = p % CBigNum(primes[i]);
                if(remain==0)return false;
        }
        return true;
}
bool TestWithSmallPrime(const CBigNum& origin, int length){
        if(size == 0){
                memset(mask, 0, sizeof(mask));
                primes[size++] = 2;
                for(int i = 3; i < MAXN; i+=2){
                        if(mask[i]==0){
                                primes[size++] = i;
                                if(size == 10000)break;
                                for(int j = i+i; j < MAXN; j+=i)
                                        mask[j] = 1;
                        }
                }
                printf("#primes = %d\n", size);
        }
        int len1=0, len2=0, len3=0;
        for(int i = 0; i < length; ++i){
                if(TestPrime(origin*(1<<i)-1)) ++len1;
                else break;
        }
        if(len1 == length) return true;
        for(int i = 0; i < length; ++i){
                if(TestPrime(origin*(1<<i)+1)) ++len2;
                else break;
        }
        if(len2 == length) return true;
        len3 = 2 * std::min(len1, len2);
        if(len1 == len2 +1) ++len3;
        if(len3 >= length) return true;
        return false;
}