segemented sieve

Author: Nadim-Mahmud

Source/Number Theory/segmented_sieve.cpp

@@ -0,0 +1,26 @@
+
+/// *** Segmented Sieve O( sqrt(up) + prime sieve )
+
+/** [l = lower limit, u = upper limit]
+*   [first generate all prime upto sqrt(upper limit)]
+*   [Checking prime
+*   n = number into that segment]
+*   if(!mark[n-l]) then it is prime
+*/
+bool mark[u-l];
+void segsiv(ll l, ll u)
+{
+    ll i,j,lt;
+    if(l==1) mark[0] = 1;
+    for(i=1; i<=in&&pr[i]*pr[i]<=u; i++){
+        lt = l/pr[i];
+        lt *= pr[i];
+        if(lt<l) lt += pr[i];
+        if(pr[i]==lt) lt += pr[i];
+        for(lt; lt<=u; lt+=pr[i]){
+            mark[lt-l] = 1;
+        }
+    }
+}
+
+