# [Rd] sum() returns NA on a long *logical* vector when nb of TRUE values exceeds 2^31

Martin Maechler maechler at stat.math.ethz.ch
Mon Feb 5 13:43:31 CET 2018

```>>>>> Martin Maechler <maechler at stat.math.ethz.ch>
>>>>>     on Thu, 1 Feb 2018 16:34:04 +0100 writes:

> >>>>> Hervé Pagès <hpages at fredhutch.org>
> >>>>>     on Tue, 30 Jan 2018 13:30:18 -0800 writes:
>
>     > Hi Martin, Henrik,
>     > Thanks for the follow up.
>
>     > @Martin: I vote for 2) without *any* hesitation :-)
>
>     > (and uniformity could be restored at some point in the
>     > future by having prod(), rowSums(), colSums(), and others
>     > align with the behavior of length() and sum())
>
> As a matter of fact, I had procrastinated and worked at
> implementing '2)' already a bit on the weekend and made it work
> - more or less.  It needs a bit more work, and I had also been considering
> replacing the numbers in the current overflow check
>
> 	if (ii++ > 1000) {	 \
> 	    ii = 0;							\
> 	    if (s > 9000000000000000L || s < -9000000000000000L) {	\
> 		if(!updated) updated = TRUE;				\
> 		*value = NA_INTEGER;					\
> 		warningcall(call, _("integer overflow - use sum(as.numeric(.))")); \
> 		return updated;						\
> 	    }								\
> 	}								\
>
> i.e. think of tweaking the '1000' and '9000000000000000L',
> the moment.
> They may look arbitrary, but are not at all: If you multiply
> them (which looks correct, if we check the sum 's' only every 1000-th
> time ...((still not sure they *are* correct))) you get  9*10^18
> which is only slightly smaller than  2^63 - 1 which may be the
> maximal "LONG_INT" integer we have.
>
> So, in the end, at least for now, we do not quite go all they way
> but overflow a bit earlier,... but do potentially gain a bit of
> speed, notably with the ITERATE_BY_REGION(..) macros
> (which I did not show above).
>
> Will hopefully become available in R-devel real soon now.
>
> Martin

After finishing that... I challenged myself that one should be able to do
better, namely "no overflow" (because of large/many
integer/logical), and so introduced  irsum()  which uses a double
precision accumulator for integer/logical  ... but would really
only be used when the 64-bit int accumulator would get close to
overflow.
The resulting code is not really beautiful, and also contains a
a comment     " (a waste, rare; FIXME ?) "
If anybody feels like finding a more elegant version without the
"waste" case, go ahead and be our guest !

Testing the code does need access to a platform with enough GB
RAM, say 32 (and I have run the checks only on servers with >
100 GB RAM). This concerns the new checks at the (current) end
of <R-devel_R>/tests/reg-large.R

In R-devel svn rev >= 74208  for a few minutes now.

Martin

```