On Sun, Jan 11, 2009 at 5:58 AM, Kevin Sopp <baraclese@googlemail.com> wrote:
(2)
mp_int<> a = 13; int b = -1; cout << (a | b) << endl; // Should be -1, right?
No, -13 is the correct answer here. You're ORing the magnitude of both numbers when using mp_ints. Unlike the built in integral types for which the answer depends on the internal binary representation of numbers (usually it's two's complement).
The interpretation of OR that you describe is consistent with libtommath (of course) but not with other arbitrary-precision-integer packages that I have tried. When I try either 13 OR -1 or (BIG(1) << 200) | -1, I get -1 from all of the following: gmp java.math.BigInteger Python's built-in long type Ruby's built-in Bignum type Likewise, all of these give me -14 for (BIG(13) ^ -1), while libtommath and mp_int give -12. -- Nathan -- Nathan