On Sun, Jun 24, 2012 at 2:21 PM, michael85 <todormi...@gmail.com> wrote:
> There's a small copy / paste gone wrong issue in the code: mpz_powm_ui(out,
> x, -1UL, n). Unfortunately, even after I remove the UL, the behavior is the
> same.
You can't pass a negative value as an unsigned long parameter. -1UL
is really to 2**32 - 1. Just create another mpz_t for the exponent and
set it to -1.
casevh
>
> Mihai
>
>
> On Sunday, June 24, 2012 10:47:36 PM UTC+2, michael85 wrote:
>>
>> Hello Everyone,
>>
>> For some reason, I am not able to understand why the following code prints
>> different results:
>>
>> mpz_t x, n, out;
>>
>> mpz_init_set_ui(x, 2UL);
>> mpz_init_set_ui(n, 7UL);
>> mpz_init(out);
>>
>> mpz_invert(out, x, n);
>> gmp_printf ("%Zd\n", out);//prints 4. 2 * 4 (mod 7) = 1. OK
>>
>> mpz_powm_ui(out, x, -1UL, n);//prints 1. 2 * 1 (mod 7) = 2. How come?
>> gmp_printf ("%Zd\n", out);
>>
>> mpz_clear(x);
>> mpz_clear(n);
>> mpz_clear(out);
>>
>> The documentation states that negative exponents are supported by mpz_powm
>> if base^-1 nod n exists. This behavior is the same as in GMP 4.1 on Windows.
>> What am I missing here?
>>
>> Best regards,
>> Mihai Todor
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