Re: [PATCH 2/2] MPI: Fix mpi_powm() when exponent is 0 and the result has no limbs

David Howells
2016-11-24T11:33:39Z

Andrey Ryabinin <ryabinin.a.a@gmail.com> wrote:

> > David Howells <dhowells@redhat.com> wrote:
> >
> >> + if (!rp) {
> >> + if (mpi_resize(res, 1) < 0)
> >
> > This is better done with RESIZE_IF_NEEDED().
> >
>
> mpi_resize() is equal to RESIZE_IF_NEEDED(), it also checks for allocated space:
>
> int mpi_resize(MPI a, unsigned nlimbs)
> {
> ....
> if (nlimbs <= a->alloced)
> return 0; /* no need to do it */

Hmmm... In that case, should your patch use mpi_resize() rather than
RESIZE_IF_NEEDED()? It's a trivial case that we should perhaps weed out much
earlier (ie. reject the key if exp<2 or mod<2), but it would make the object
file slightly smaller not to do the test twice.

David