[Rcpp-devel] short, unsigned short, long, unsigned long, long double

[Douglas Bates]

On Tue, Apr 6, 2010 at 7:15 AM, Douglas Bates <bates at stat.wisc.edu> wrote:
> On Tue, Apr 6, 2010 at 6:54 AM, Romain Francois
> <romain at r-enthusiasts.com> wrote:
>> Hello,
>>
>> I have added support for these primitive types in Rcpp, so that one can
>> wrap containers such as :
>>
>> std::vector<short>, ...
>>
>> Is this something that should be protected in case there is no "short",
>> "long", etc ?
>
> You can check in R's .Machine object on the various sizes for which R
> scans.  It can tell you if there is a difference between long and long
> long or between double and long double.  It does not list anything
> regarding short.  The sum of double.digits and double.exponent is the
> number of bits in a double.  Generally log(.Machine$integer.max, 2) is
> 1 less than the number of bits in an int.
>
>
>> str(.Machine)
> List of 18
>  $ double.eps           : num 2.22e-16
>  $ double.neg.eps       : num 1.11e-16
>  $ double.xmin          : num 2.23e-308
>  $ double.xmax          : num 1.80e+308
>  $ double.base          : int 2
>  $ double.digits        : int 53
>  $ double.rounding      : int 5
>  $ double.guard         : int 0
>  $ double.ulp.digits    : int -52
>  $ double.neg.ulp.digits: int -53
>  $ double.exponent      : int 11
>  $ double.min.exp       : int -1022
>  $ double.max.exp       : int 1024
>  $ integer.max          : int 2147483647
>  $ sizeof.long          : int 4
>  $ sizeof.longlong      : int 8
>  $ sizeof.longdouble    : int 12
>  $ sizeof.pointer       : int 4
>> log(.Machine$integer.max, 2)
> [1] 31

Perhaps I am not answering the question that you asked - that sort of
thing happens when answering email while still on the first cup of
coffee.  More helpful might be the comments in the limits include file
for libstdc++ on Debian/Ubuntu

// The numeric_limits<> traits document implementation-defined aspects
// of fundamental arithmetic data types (integers and floating points).
// From Standard C++ point of view, there are 13 such types:
//   * integers
//         bool						        (1)
//         char, signed char, unsigned char			(3)
//         short, unsigned short				(2)
//         int, unsigned					(2)
//         long, unsigned long					(2)
//
//   * floating points
//         float						(1)
//         double						(1)
//         long double						(1)
//
// GNU C++ understands (where supported by the host C-library)
//   * integer
//         long long, unsigned long long			(2)
//
// which brings us to 15 fundamental arithmetic data types in GNU C++.

So it looks like short is part of standard C++ but not long long.