Re: Bug in huge simplehash

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.

Greetings,

Andres Freund