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perftune/sieve.c

@@ -24,7 +24,7 @@ int *sieve(int n) {
   //use other primes
   for (int i = 3; i <= n; i+=2) {
     if(!is_prime[i]) continue;  //use prime i only
-    
+    if(i*(i+2) > n) break;
     //枚举优化 todo
     for(int j = i*(i+2); j<=n; j = j+i+i){
       is_prime[j] = false;