[Rcpp-devel] long long

[Romain Francois]

Le 19/09/13 15:30, Dirk Eddelbuettel a écrit :
>
> On 19 September 2013 at 14:18, Romain Francois wrote:
> | (rebrand as a Rcpp-devel question)
>
> I just re-explained it on our internal rcpp-core list. The same points were
> all made here too circa 2010 and are in the list archives.

Sure. You explained what you think is right. I disagree. Let me explain 
a bit more then.

> In short, we are up against a CRAN Policy which wants
>
>    i)   "standards compliant code" put unfortunately insists on a 15 year old
>         standard (C++98)
>
>    ii)  "portable code" as it maintains that there are compilers not named g++
>         or clang++ which matter (which I sort of agree with on theoretical
>         grounds, in practice I'd be ready to differ).
>
> But in short it is not our call.  If we want Rcpp to be on CRAN (and I
> maintain that we do) then we do NOT get long long.  At least not yet.
>
> But I guess by the time we all are retired CRAN may allow the C++11 standard.
>
> Dirk

What I want is to change this:

#if defined(__GNUC__)
#if defined(__GXX_EXPERIMENTAL_CXX0X__) || (defined (__clang__) && 
defined(__LP64__))
#ifdef __LONG_LONG_MAX__
     __extension__ typedef long long int rcpp_long_long_type;
     __extension__ typedef unsigned long long int rcpp_ulong_long_type;
     #define RCPP_HAS_LONG_LONG_TYPES
#endif
#endif
#endif


to this:

#if defined(__GNUC__) &&  defined(__LONG_LONG_MAX__)
     __extension__ typedef long long int rcpp_long_long_type;
     __extension__ typedef unsigned long long int rcpp_ulong_long_type;
     #define RCPP_HAS_LONG_LONG_TYPES
#endif


In both cases, we have artifacts of non portability, i.e. the 
__extension__ thing, but in both cases they are hidden behind 
defined(__GNUC__) so only enabled for gcc compatible compiler (so gcc 
and clang).


But in what I propose, we can actually make something useful for long 
long types, which we would have to use as rcpp_long_long_type for more 
settings. For example, with this version of gcc on the mac, I have long 
long but I can't use it:

$ gcc --version
i686-apple-darwin11-llvm-gcc-4.2 (GCC) 4.2.1 (Based on Apple Inc. build 
5658) (LLVM build 2336.11.00)

If I follow your argument, neither what is currently in Rcpp not what I 
propose should be in Rcpp.

Writing portable code is about settling on the lowest common denominator 
but enable more things for more capable compilers when we know we use them.


Anyway, i can install Rcpp on both my OSX machine and your ubuntu with 
gcc 4.4.7-2, compiling it with -pedantic in both cases and not get these 
warnings.

And as long as we don't actually have "long long" in code, but use 
"rcpp_long_long_type" then we are fine :

 > demangle( "rcpp_long_long_type" )
[1] "long long"
 >
 > demangle( "long long" )
file76776fc6e118.cpp: In function ‘SEXPREC* manipulate_this_type()’:
file76776fc6e118.cpp:8: warning: ISO C++ 1998 does not support ‘long long’
[1] "long long"

So we get the warnings because we explicitely write "long long" in code.


What I propose is as much (un)portable as what we have, it just is more 
useful when it can be.

Romain

-- 
Romain Francois
Professional R Enthusiast
+33(0) 6 28 91 30 30