[Rd] survival bug? - solved

[Tomas Kalibera]

On 3/5/20 5:39 PM, Therneau, Terry M., Ph.D. via R-devel wrote:
>    I ended up finding the issue by a focused code review.
>
> Once in the past, I had a version that would fail under one architecture but not another,
> in that case some help from Brian Ripley pointed me to the offending line of C code.
> That line read, but did not write, at an invalid memory location.   Starting with the
> question of "what C routines have I added or modified most recently" along with where the
> fault appeared to occur in my test suite, I started reading C code and found one.
> Revised code passes tests on the winbuilder site.
>
> For the curious, I had a line asking "is this patient id different than the last patient
> id" in the C routine underneath survcheck(); I'm making sure that patients don't go
> backwards in time. Essentially
>    for (i=0; i< n; i) {
>        if (id[i] != id[i-1] )  { ...}
>
> It is still a surprise to me that just LOOKING at this out of range element would cause a
> failure,  [i-1] never appears on the left hand side of any expressions in the ... chunk
> above. Nevertheless, it was an error.   Que sera sera

In principle out of bounds access to an array, even reading, may not 
only return any value that may be there, but cause a memory protection 
failure (the memory there is not accessible) or have some other impact. 
Reads from memory can also have side effects (other than crashing your 
process).

Tomas

>
> A strong thanks to those who gave solid suggestions for bringing up a local copy of Windows.
>
> Terry T
>
>>>> My latest submission of survival3.1-10 to CRAN fails  a check, but only on
>>>> windows, which
>>>> I don't use.
>>>> How do I track this down?
>>>> The test in question works fine on my Linux box.
>>>>
>>>> Terry
>>>>
>>>>
>>>>
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