Thanks for pointing that out. I just noticed it myself, after pulling hairs
out for a few hours :( I guess this is a documentation bug, or something...
Regards,
Mihai
On Sunday, June 24, 2012 11:29:36 PM UTC+2, casevh wrote:
>
> 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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