From f478d6feca0d20aa0ab086497d1315ca724ec5cc Mon Sep 17 00:00:00 2001
From: Dmitry Kokorin <dmitry@kokorin.org>
Date: Fri, 1 Apr 2016 17:25:34 +0300
Subject: [PATCH] sieve: improvement

---
 cpp/sieve/sieve.cpp | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/cpp/sieve/sieve.cpp b/cpp/sieve/sieve.cpp
index bab3b1f..cddc280 100644
--- a/cpp/sieve/sieve.cpp
+++ b/cpp/sieve/sieve.cpp
@@ -1,5 +1,6 @@
 #include "sieve.h"
 
+
 namespace sieve {
 
 using namespace std;
@@ -10,19 +11,21 @@ primes_t primes(size_t n)
 
     vector<char> sieve(n, false);
 
-    for (size_t p = 2; p < n; ++p) {
+    for (size_t p = 2, p2 = 2*2; p2 < n; ++p, p2 = p*p) {
 
         if (sieve[p])
             continue;
 
-        result.push_back(p);
-
-        for (size_t i = p*p; i < n; i += p) {
+        for (size_t i = p2; i < n; i += p) {
 
             sieve[i] = true;
         }
     }
 
+    for (size_t i = 2; i < n; ++i)
+        if (!sieve[i])
+            result.push_back(i);
+
     return result;
 }