[Rcpp-devel] Subsetter uses int for indexing (among other issues)?

[Kevin Ushey]

I agree we should be using R_xlen_t here. As always, PRs are welcome.

You might want to file this at https://github.com/RcppCore/Rcpp/issues
just so it doesn't get lost.

Thanks,
Kevin

On Tue, Nov 6, 2018 at 11:23 PM Qiang Kou <qkou at qkou.info> wrote:
>
> Hi, William,
>
> Can you give us a small piece of code to reproduce the error? That will ease our discussion.
>
> Best,
>
> KK
>
> On Tue, Nov 6, 2018 at 10:46 PM William Nolan <will at landale.net> wrote:
>>
>> Hi all,
>>
>> Longtime user and lurker here.
>>
>> I got "index error" thrown by Rcpp when trying to subset a matrix with width * height == 644764 * 3776 greater than MAXINT:
>>
>> Allocating 647764 x 3776 matrix...
>> Catchpoint 1 (exception thrown), 0x00007ffff4baa920 in __cxa_throw () from /usr/lib64/libstdc++.so.6
>> #1  0x0000000000473a05 in Rcpp::stop<>(char const*) (fmt=0x7fffe7bc3545 "index error")
>>     at /home/nolanw/R/x86_64-redhat-linux-gnu-library/3.5/Rcpp/include/Rcpp/exceptions/cpp11/exceptions.h:52
>> 52          throw Rcpp::exception( tfm::format(fmt, std::forward<Args>(args)... ).c_str() );
>> (gdb) down
>> #0  0x00007ffff4baa920 in __cxa_throw () from /usr/lib64/libstdc++.so.6
>> (gdb) up
>> #1  0x0000000000473a05 in Rcpp::stop<>(char const*) (fmt=0x7fffe7bc3545 "index error")
>>     at /home/nolanw/R/x86_64-redhat-linux-gnu-library/3.5/Rcpp/include/Rcpp/exceptions/cpp11/exceptions.h:52
>> 52          throw Rcpp::exception( tfm::format(fmt, std::forward<Args>(args)... ).c_str() );
>> (gdb) up
>> #2  0x00007fffe7bb75a6 in Rcpp::SubsetProxy<14, Rcpp::PreserveStorage, 13, true, Rcpp::Vector<13, Rcpp::PreserveStorage> >::check_indices (this=0x7fffffffc450, x=0x13f9920,
>>     n=3751, size=-1849010432) at /home/nolanw/R/x86_64-redhat-linux-gnu-library/3.5/Rcpp/include/Rcpp/vector/:138
>> 138                     stop("index error");
>> (gdb) up
>> #3  0x00007fffe7bb6a3c in Rcpp::SubsetProxy<14, Rcpp::PreserveStorage, 13, true, Rcpp::Vector<13, Rcpp::PreserveStorage> >::get_indices (this=0x7fffffffc450, t=...)
>>     at /home/nolanw/R/x86_64-redhat-linux-gnu-library/3.5/Rcpp/include/Rcpp/vector/Subsetter.h:149
>> 149             check_indices(ptr, rhs_n, lhs_n);
>> (gdb) l
>> 144         #endif
>> 145
>> 146         void get_indices( traits::identity< traits::int2type<INTSXP> > t ) {
>> 147             indices.reserve(rhs_n);
>> 148             int* ptr = INTEGER(rhs);
>> 149             check_indices(ptr, rhs_n, lhs_n);
>> 150             for (int i=0; i < rhs_n; ++i) {
>> 151                 indices.push_back( rhs[i] );
>> 152             }
>> 153             indices_n = rhs_n;
>>
>> As we can see from the stack trace and below, lhs.size() is negative when cast to int:
>>
>> (gdb) p (int)(lhs.size())
>> $12 = -1849010432
>>
>> This is all coming from the assignment (via operator []) of the subsetting of one matrix to another matrix's subset:
>>
>> (static_cast<NumericVector&>(mat))[lhsI] = (static_cast<NumericVector&>(signals))[rhsI];
>>
>> (lhsI and rhsI are IntegerVector's)
>>
>> Now, setting aside whether I *should* be doing that -- what I *do* see in Subsetter.h (including what I understand to be the most recent version, 1.0.0 from github) is the use of int for indices all over the place in this file, including in the member variable:
>>
>> std::vector<int> indices;
>>
>> Is there any reason why the indices that Subsetter uses internally shouldn't be size_t or an equivalently capable type like R_xlen_t?
>> For example, Subsetter's check_indices function takes int's as arguments, while Vector's size method returns R_xlen_t.
>>
>> I'll change my code to manually copy elements via operator() using the row/column arguments for now.  Seems like Subsetter is maybe not quite ready for prime time.
>>
>>
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