Added algorithm Fermat factorization

diff --git a/src/primefactors.cpp b/src/primefactors.cpp
index 20c77bd..7de4e33 100644 (file)
--- a/src/primefactors.cpp
+++ b/src/primefactors.cpp
@@ -76,6 +76,30 @@ void factor_int(mpz_class N, mpz_class* d, unsigned long& nooffactors, mpz_class
 
 }
 
+/* Algorithm C from Knuth's Art of Computer Programm 2: Seminumerical Algorithms */
+/* Fermat like factorization */
+/* page 387 */
+void factor_int2(mpz_class N)
+{
+       unsigned long a = (unsigned long)(2*sqrt(N.get_ui())+1);
+       unsigned long b = 1;
+       signed long r = (signed long)((unsigned long)(sqrt(N.get_ui()))*(unsigned long)(sqrt(N.get_ui()))-N.get_ui());
+
+       while(r!=0)
+       {
+               r = r+a;
+               a = a+2;
+
+               while(r > 0)
+               {
+                       r = r-b;
+                       b = b+2;
+               }
+
+       }
+       cout << "Found prime-factors: " << (a-b)/2 << " and " << ((a+b-2)/2) << endl;
+}
+
 int main()
 {
    mpz_class N;
@@ -113,6 +137,8 @@ int main()
           cout << factors[i] << " ";
    cout << endl;
 
+   factor_int2(N);
+
    return (0);
 }