64 bit integers

[romainfrancois]

From Murray:

A vector of 64-bit integers in C++ code should be either returned as

1. An integer vector (if all values are < INT_MAX in the C code) corresponding to R's integer type.

2. A numeric vector (if all values are < 1L << 53 such that they can be stored precisely in a double without losing any digits of precision) corresponding to R's numeric type.

3. A vector of strings (if at least 1 value > 1L << 53 such that returning a numeric would lose precision in the result. e.g. 64-bit fingerprints, userids, network addresses or other things can not be stored in a numeric accurately.

Sorry no patch, I work around this in my application code currently before calling Rcpp::wrap().

[romainfrancois]

Distinguishing at runtime based on the values would be quite expensive.

Perhaps we can emit data compatible with the bit64 package. i.e. something that looks like a numeric vector but uses the 64 bits of the double to store the 64 bits of a 64 bits integer.

[dselivanov]

Just want to put here related rcpp-devel discussion (I think could be someone looking how to use bit64 with Rcpp). Mb worth to put method described by @kevinushey to Rcpp FAQ.

#include <Rcpp.h>
using namespace Rcpp;

// [[Rcpp::export]]
NumericVector timesTwo(NumericVector input) {

  R_xlen_t n = input.size();
  NumericVector output = no_init(n);

  long long* pInput  = (long long*) dataptr(input);
  long long* pOutput = (long long*) dataptr(output);
  for (R_xlen_t i = 0; i < n; i++)
    *pOutput++ = *pInput++ * 2;

  output.attr("class") = "integer64";
  return output;
}

/*** R
library(bit64)
object <- as.integer64(1:16)
timesTwo(object)
*/

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