rework long long detection

Author: kevinushey

inst/include/Rcpp/longlong.h

@@ -22,35 +22,33 @@
 #ifndef RCPP_LONG_LONG_H
 #define RCPP_LONG_LONG_H
 
-// 'long long' is a C99 extension and (as of fall 2013) still
-// forbidden by CRAN which stick with the C++98 standard predating it.
-// One way to get 'long long' is to switch to C++11, another is to use
-// clang++ from the llvm project.
-#ifdef __GNUC__
-#if defined(__GXX_EXPERIMENTAL_CXX0X__) || (defined (__clang__) && defined(__LP64__))
-
-#if defined(__GNUC__) &&  defined(__LONG_LONG_MAX__)
+// long long is explicitly available to C++11 (and above) compilers
+#if __cplusplus >= 201103L
+
+typedef long long int rcpp_long_long_type;
+typedef unsigned long long int rcpp_ulong_long_type;
+# define RCPP_HAS_LONG_LONG_TYPES
+
+// GNU compilers may make 'long long' available as an extension
+// (note that __GNUC__ also implies clang, MinGW)
+#elif defined(__GNUC__)
+
+// check to see if 'long long' can be used as an extension
+# if defined(_GLIBCXX_USE_LONG_LONG)
+
 __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
+#  define RCPP_HAS_LONG_LONG_TYPES
 
-// The Rtools toolchain provides long long on 64bit Windows,
-// but using those types directly in C++98 mode can trigger
-// compiler warnings:
-//
-//   warning: ISO C++ 1998 does not support 'long long' [-Wlong-long]
-//
-// fortunately, glibc provides these types as aliases for int64_t
-// and uint64_t, which we can use as extensions in C++98 mode
-#if defined(_WIN32) && defined(_GLIBCXX_HAVE_INT64_T) && defined(_GLIBCXX_HAVE_INT64_T_LONG_LONG)
-# include <stdint.h>
+// check to see if 'long long' is an alias for 'int64_t'
+# elif defined(_GLIBCXX_HAVE_INT64_T) && defined(_GLIBCXX_HAVE_INT64_T_LONG_LONG)
+#  include <stdint.h>
 typedef int64_t rcpp_long_long_type;
 typedef uint64_t rcpp_ulong_long_type;
-#define RCPP_HAS_LONG_LONG_TYPES
+#  define RCPP_HAS_LONG_LONG_TYPES
+
+# endif
 #endif
 
+
 #endif