[Rd] Surprising results from INTEGER_GET_REGION with ALTREP object

[Ralf Stubner]

Dear Listmembers,

wanting to learn more about ALTREP I wrote the following function to
extract a subsequence from an integer vector:

#include <Rinternals.h>

SEXP integer_get_region(SEXP _x, SEXP _i, SEXP _n) {
  int i = INTEGER(_i)[0];
  int n = INTEGER(_n)[0];
  SEXP result = PROTECT(Rf_allocVector(INTSXP, n));
  INTEGER_GET_REGION(_x, i, n, INTEGER(result));
  UNPROTECT(1);
  return result;
}

For "shorter" vectors, the result is as expected:

> dyn.load("altrep_int_region.so")
> .Call("integer_get_region", 1:1e9, 0L, 10L)
 [1]  1  2  3  4  5  6  7  8  9 10

But not for "longer" vectors:

> .Call("integer_get_region", 1:1e10, 0L, 10L)
 [1]          0 1072693248          0 1073741824          0 1074266112
 [7]          0 1074790400          0 1075052544


Am I doing something wrong or is this a bug? I am using

> R.version.string
[1] "R version 3.5.2 (2018-12-20)"

Thanks
Ralf

-- 
Ralf Stubner
Senior Software Engineer / Trainer

daqana GmbH
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