On 14.12.2011 17:19, peter dalgaard wrote:
On Dec 14, 2011, at 16:19 , John C Nash wrote:
Following this thread, I wondered why nobody tried cumsum to see where the
integer
overflow occurs. On the shorter xx vector in the little script below I get a
message:
Warning message:
Integer overflow in 'cumsum'; use 'cumsum(as.numeric(.))'
But sum() does not give such a warning, which I believe is the point of
contention. Since
cumsum() does manage to give such a warning, and show where the overflow
occurs, should
sum() not be able to do so? For the record, I don't class the non-zero answer
as an error
in itself. I regard the failure to warn as the issue.
It (sum) does warn if you take the two "halves" separately. The issue is that
the overflow is detected at the end of the summation, when the result is to be saved to
an integer (which of course happens for all intermediate sums in cumsum)
x<- c(rep(1800000003L, 10000000), -rep(1200000002L, 15000000))
sum(x[1:10000000])
[1] NA
Warning message:
In sum(x[1:1e+07]) : Integer overflow - use sum(as.numeric(.))
sum(x[10000001:25000000])
[1] NA
Warning message:
In sum(x[10000001:1.5e+07]) : Integer overflow - use sum(as.numeric(.))
sum(x)
[1] 4996000
There's a pretty easy fix, essentially to move
if(s> INT_MAX || s< R_INT_MIN){
warningcall(call, _("Integer overflow - use sum(as.numeric(.))"));
*value = NA_INTEGER;
}
inside the summation loop. Obviously, there's a speed penalty from two FP
comparisons per element, but I wouldn't know whether it matters in practice for
anyone.
I don't think I am interested in where the overflow happens if I call
sum()...
Uwe
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