FW: [Rd] sum overflow (PR#1091)

[Warnes, Gregory R]

> From: David Smith [mailto:dsmith@insightful.com]
>> From: Prof Brian Ripley
>>
>> If you use integers you need to be aware of the consequences.  It's a
>> feature not a bug.
>
> Perhaps, but maybe a more useful feature would be to signal to the user
when
> such an overflow occurs?  Sv4 does this by returning NA for overflow
integer
> results:
> 
> > a <- (1:1000)
> > b <- (1:1000)
> > sum(a * a) * sum(b * b)
> [1] NA
> 
> When this was introduced in S-PLUS 5, we discovered some overflow errors
we
> were previously unaware of in S-PLUS (by noticing NAs in the results).

This is a first step in the right direction.  I think that having overflows
generate of NA's should be augmented by a warning or an error message.
Thus we would get something like:

> a <- (1:1000)
> b <- (1:1000)
> sum(a * a) * sum(b * b)
Warning messages: 
Integer overflow produced NA's in: .Primitive("*") 
> [1] NA

Now, the problem will be clear to the user, and many users will immediately
see how to get around it.

-Greg


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