Strange bit of code in ulong_extras/is_probabprime.c

[mhogrefe]

Hello,

I'm trying to understand some code in ulong_extras/is_probabprime.c, and I found something unusual. It doesn't seem to be causing any bugs, so either I'm misunderstanding something, or the code is never executed, or it's executed but (unexpectedly?) works.

In the code for n_is_probabprime_lucas, on line 425, n_mulmod_precomp is being called with ninv, which is a ulong created by n_preinvert_limb. But typically n_mulmod_precomp is called with a double generated by n_precompute_inverse instead. That double is typically between 0 and 1, so it's strange that it's cast from a ulong in this case.

Compare the code for n_is_probabprime_fibonacci, on line 258, where n_precompute_inverse is paired with n_mulmod_precomp and n_preinvert_limb with n_mulmod2_preinv, as expected.

Is this intentional?

Thanks,
Mikhail Hogrefe

[albinahlback]

Indeed, it very much looks like a bug. However, we do get code coverage there.