[PD] unexpected [array max] and [array min] behavior
Matt Barber
brbrofsvl at gmail.com
Sun Sep 13 02:18:31 CEST 2015
Thanks again. Can you confirm that a range with onset greater than n-1
should be empty, and not a range with just the (n-1) item? I'm building
some abstractions with these, and I want range behavior to be consistent
with those in the [array] objects.
Thanks!
M
On Fri, Sep 11, 2015 at 7:50 PM, Miller Puckette <msp at ucsd.edu> wrote:
> I think it's correct to output negative infinity as the maximum value of
> the
> empty set, since if A is a subset of B, max(A) <= max(B), so the max of the
> empty set should be less than any number. Hovever, using "1e30" for
> infinity
> is stupid and arbitrary - I do that sort of thing only because it's so
> poisonous in a real-time context when actual "inf" values start getting
> around
> the objects...
>
> The second thing you brought up is a mistake. OTOH on revisiting this, I
> think the empty set should result in an output of (the impossible) -1 so
> that it can be easily checked for using select. Also using "firstitem"
> would give a bad result if used on an array of structs with more than one
> member - so a but more surgery is needed here...
>
> more soon, off to a party to welcome the excellent Natacha Diels to our
> department :)
>
> M
>
> On Fri, Sep 11, 2015 at 04:14:47PM -0400, Matt Barber wrote:
> > Thanks for the fix in 0.46.7. There are a couple more subtle problems
> > having to do with bounds checking (one of which may be there by design).
> > Bounds checking occurs in the function array_rangeop_getrange() starting
> > line 536:
> >
> > firstitem = x->x_onset;
> > if (firstitem < 0)
> > firstitem = 0;
> > else if (firstitem > a->a_n)
> > firstitem = a->a_n;
> > if (x->x_n < 0)
> > nitem = a->a_n - firstitem;
> > else
> > {
> > nitem = x->x_n;
> > if (nitem + firstitem > a->a_n)
> > nitem = a->a_n - firstitem;
> > }
> >
> >
> > So unlike tabread which clips indices from 0 to n-1, this clips the onset
> > from 0 to n, which means an onset greater than (n-1) gets a range with 0
> > items. I think this might be by design, but I wanted to check because a
> > range with 0 items does something funny in the min/max array objects.
> >
> > So first off, in these lines (starting line 746):
> >
> > for (i = 0, besti = 0, bestf= -1e30, itemp = firstitem;
> > i < nitem; i++, itemp += stride)
> > if (*(t_float *)itemp > bestf)
> > bestf = *(t_float *)itemp, besti = i;
> >
> > If the input range has 0 items (i.e. if nitems is set to zero manually,
> or
> > if the onset is greater than n-1), the for-loop condition i < nitem is
> > never true, so the value output is going to be the bestf init value -1e30
> > (likewise with +1e30 in the min function). Since this a value that
> doesn't
> > point to anything in the array, I wonder if it would be better not to
> > output anything (or maybe a bang) in those cases.
> >
> >
> > Second, the value x->x_rangeop.x_onset is not bounds checked, so when you
> > do this (line 750):
> >
> > outlet_float(x->x_out2, besti + x->x_rangeop.x_onset);
> >
> >
> > if x_rangeop.x_onset iss out of range, you're going to output an
> erroneous
> > index value, which could be negative or greater than n. firstitem is
> > bounds-checked from the onset by array_rangeop_getrange() -- would it be
> > possible to use that instead?
> >
> >
> > This suite is really a wonderful addition to Pd, and adds so much new
> > functionality to vanilla.
> > Many cheers!
> >
> > Matt
> >
> >
> > On Fri, Sep 4, 2015 at 8:11 PM, Miller Puckette <msp at ucsd.edu> wrote:
> >
> > > Yep :)
> > >
> > > M
> > >
> > > On Fri, Sep 04, 2015 at 07:46:30PM -0400, Matt Barber wrote:
> > > > Thanks.
> > > >
> > > > I meant to say that there was the same problem in [array min], but
> you
> > > > probably caught it in your fix.
> > > >
> > > > Best,
> > > >
> > > > Matt
> > > >
> > > > On Fri, Sep 4, 2015 at 7:19 PM, Miller Puckette <msp at ucsd.edu>
> wrote:
> > > >
> > > > > Yep... thanks. Fixed in git - may take some time for me to get
> out a
> > > new
> > > > > compiled version (other stuff to fix too :)
> > > > >
> > > > > M
> > > > >
> > > > >
> > > > > On Fri, Sep 04, 2015 at 05:51:15PM -0400, Matt Barber wrote:
> > > > > > Hi list,
> > > > > >
> > > > > > I've been playing around with the new(ish) [array] object suite
> in
> > > > > vanilla
> > > > > > 0.46.6. Forgive me if this is already a known issue, but it looks
> > > like
> > > > > the
> > > > > > min and max arguments aren't working properly.
> > > > > >
> > > > > > The second inlet (setting the number of points to search) works
> as
> > > > > > expected. The first inlet doesn't update: it seems to be set to
> 0 no
> > > > > matter
> > > > > > what (although the index outlet is updated, but not as expected).
> > > > > >
> > > > > > I think I see the problem in x_array.c
> > > > > >
> > > > > > The max object is defined line 723:
> > > > > >
> > > > > > typedef struct _array_max
> > > > > > {
> > > > > > t_array_rangeop x_rangeop;
> > > > > > t_outlet *x_out1; /* value */
> > > > > > t_outlet *x_out2; /* index */
> > > > > > int x_onset; /* search onset */
> > > > > > } t_array_max;
> > > > > >
> > > > > >
> > > > > > And the bang and float methods starting 740:
> > > > > >
> > > > > > static void array_max_bang(t_array_max *x)
> > > > > > {
> > > > > > char *itemp, *firstitem;
> > > > > > int stride, nitem, i, besti;
> > > > > > t_float bestf;
> > > > > > if (!array_rangeop_getrange(&x->x_rangeop, &firstitem,
> &nitem,
> > > > > &stride))
> > > > > > return;
> > > > > > for (i = 0, besti = 0, bestf= -1e30, itemp = firstitem;
> > > > > > i < nitem; i++, itemp += stride)
> > > > > > if (*(t_float *)itemp > bestf)
> > > > > > bestf = *(t_float *)itemp, besti = i;
> > > > > > outlet_float(x->x_out2, besti+x->x_onset);
> > > > > > outlet_float(x->x_out1, bestf);
> > > > > > }
> > > > > >
> > > > > > static void array_max_float(t_array_max *x, t_floatarg f)
> > > > > > {
> > > > > > x->x_onset = f;
> > > > > > array_max_bang(x);
> > > > > > }
> > > > > >
> > > > > >
> > > > > > In the float method it looks like the onset is never actually
> > > assigned in
> > > > > > the x_rangeop member of the t_array_max struct, so
> > > array_rangeop_getrange
> > > > > > can't set the firstitem pointer to anything but its init value.
> > > > > >
> > > > > >
> > > > > > Thanks,
> > > > > >
> > > > > > Matt
> > > > >
> > > > > > _______________________________________________
> > > > > > Pd-list at lists.iem.at mailing list
> > > > > > UNSUBSCRIBE and account-management ->
> > > > > http://lists.puredata.info/listinfo/pd-list
> > > > >
> > > > >
> > >
> > > > _______________________________________________
> > > > Pd-list at lists.iem.at mailing list
> > > > UNSUBSCRIBE and account-management ->
> > > http://lists.puredata.info/listinfo/pd-list
> > >
> > >
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.puredata.info/pipermail/pd-list/attachments/20150912/2f500e7f/attachment.html>
More information about the Pd-list
mailing list