Re: Bug in huge simplehash

Em sex., 13 de ago. de 2021 às 07:15, Andres Freund <andres(at)anarazel(dot)de>
escreveu:

> Hi,
>
> On 2021-08-13 12:44:17 +0300, Yura Sokolov wrote:
> > Andres Freund писал 2021-08-13 12:21:
> > > Any chance you'd write a test for simplehash with such huge amount of
> > > values? It'd require a small bit of trickery to be practical. On
> systems
> > > with MAP_NORESERVE it should be feasible.
> >
> > Which way C structures should be tested in postgres?
> > dynahash/simplhash - do they have any tests currently?
> > I'll do if hint is given.
>
> We don't have a great way right now :(. I think the best is to have a
> SQL callable function that uses some API. See e.g. test_atomic_ops() et
> al in src/test/regress/regress.c
>
>
> > > > static inline void
> > > > -SH_COMPUTE_PARAMETERS(SH_TYPE * tb, uint32 newsize)
> > > > +SH_COMPUTE_PARAMETERS(SH_TYPE * tb, uint64 newsize)
> > > > {
> > > > uint64 size;
> > > >
> > > > @@ -322,11 +322,7 @@ SH_COMPUTE_PARAMETERS(SH_TYPE * tb, uint32
> > > > newsize)
> > > >
> > > > /* now set size */
> > > > tb->size = size;
> > > > -
> > > > - if (tb->size == SH_MAX_SIZE)
> > > > - tb->sizemask = 0;
> > > > - else
> > > > - tb->sizemask = tb->size - 1;
> > > > + tb->sizemask = (uint32)(size - 1);
> > >
> > > ISTM using ~0 would be nicer here?
> >
> > I don't think so.
> > To be rigid it should be `~(uint32)0`.
> > But I believe it doesn't differ from `tb->sizemask = (uint32)(size - 1)`
> > that is landed with patch, therefore why `if` is needed?
>
> Personally I find it more obvious to understand the intended behaviour
> with ~0 (i.e. all bits set) than with a width truncation.
>
https://godbolt.org/z/57WcjKqMj
The generated code is identical.

regards,
Ranier Vilela