strange results with 'power' operator in c++

[Pierre Colombier]

this is my test file "main.cc"

#include <iostream>
using namespace std;
#include <gmpxx.h>
int main (void)
{ 
 mpz_class x, p, q, eq, ep;
 x=2;
 p=0;
 q=0;
 ep=19;
 eq=27;
 cout << "X=" <<x <<"\n";
 cout << "P=" << p << "\n";
 cout << "Q=" << q << "\n";
 cout << "EP=" << ep << "\n";
 cout << "EQ=" << eq << "\n";
 p=x^ep;
 q=x^eq;
 cout << "----\n";
 cout << "P=" << p << "\n";
 cout << "Q=" << q << "\n";
 return 0;
}

it produces :

# g++ main.cc -lgmpxx -lgmp -Wall
# ./a.out
X=2
P=0
Q=0
EP=19
EQ=27
----
P=17
Q=25
#

why P=17 and Q=25 ???
should be P=524288 and Q=2097152
(operations + - * / % works well is there a problem with ^ )