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 11:24:20 up  1:20,  1 user,  load average: 0.52, 0.64, 0.82

perftune/sieve.c

@@ -10,6 +10,8 @@ static int  primes[N];
 
 int *sieve(int n) {
   assert(n + 1 < N);
+  int *p = primes; *p++ = 2;// primelist ini
+
   is_prime[1] = true; is_prime[2] = true; is_prime[3] = true; //ini
   
   //ini tobe improved
@@ -22,20 +24,24 @@ int *sieve(int n) {
     is_prime[j] = false;
 
   //use other primes
+  int pi;
   for (int i = 3; i <= n; i+=2) {
     if(!is_prime[i]) continue;  //use prime i only
-    if(i*i > n) break;
+    //到这里确定是质数
+      *p++ = i;
+    //end
+    if(i*i > n) {pi = i; break;}
     //枚举优化 todo
     for(int j = i*i; j<=n; j = j+i+i){
       is_prime[j] = false;
     }
   }
 
-  int *p = primes;
-  for (int i = 2; i <= n; i++)
+  for (int i = pi; i <= n; i+=2) //减少质数判断的访存。//这里还需要处理大于根号级别的质数
     if (is_prime[i]) {
       *p++ = i;
     }
+
   *p = 0;
   return primes;
 }