Use xtl::endianness instead of bundling it

Author: serge-sans-paille

include/xtensor/xnpy.hpp

@@ -15,6 +15,7 @@
 // relicensed from MIT License with permission
 
 #include <xtl/xsequence.hpp>
+#include <xtl/xplatform.hpp>
 
 #include <algorithm>
 #include <complex>
@@ -43,24 +44,9 @@ namespace xt
     namespace detail
     {
 
-        /* Test for endianess. Compiler can optimize that to a single constant. */
-        static inline bool is_big_endian()
-        {
-            uint32_t utmp = 0x01020304;
-            char btmp[sizeof(utmp)];
-            std::memcpy(&btmp[0], &utmp, sizeof(utmp));
-            const bool big_endian = btmp[0] == 0x01;
-            return big_endian;
-        }
-
         const char magic_string[] = "\x93NUMPY";
-        const std::size_t magic_string_length = 6;
-
-        const char little_endian_char = '<';
-        const char big_endian_char = '>';
-        const char no_endian_char = '|';
+        const std::size_t magic_string_length = sizeof(magic_string) - 1;
 
-        const char host_endian_char = (is_big_endian() ? big_endian_char : little_endian_char);
 
         template <class O>
         inline void write_magic(O& ostream,
@@ -126,9 +112,23 @@ namespace xt
         }
 
         template <class T>
-        constexpr char get_endianess()
+        inline char get_endianess()
         {
-            return sizeof(T) <= sizeof(char) ? no_endian_char : host_endian_char;
+            constexpr char little_endian_char = '<';
+            constexpr char big_endian_char = '>';
+            constexpr char no_endian_char = '|';
+
+            if(sizeof(T) <= sizeof(char))
+              return no_endian_char;
+
+            switch(xtl::endianness()) {
+              case xtl::endian::little_endian:
+                return little_endian_char;
+              case xtl::endian::big_endian:
+                return big_endian_char;
+              default:
+                return no_endian_char;
+            }
         }
 
         template <class T>

test/test_xnpy.cpp

@@ -18,10 +18,17 @@
 namespace xt
 {
     std::string get_load_filename(std::string const& npy_prefix, layout_type lt = layout_type::row_major) {
-      using detail::is_big_endian;
       std::string lts = lt == layout_type::row_major ? "" : "_fortran";
-      std::string endianess = is_big_endian() ? ".be" : ".le";
-      return npy_prefix + lts + endianess + ".npy";
+      std::string endianness;
+      switch(xtl::endianness()) {
+        case xtl::endian::big_endian:
+          endianness = ".be";
+          break;
+        case xtl::endian::little_endian:
+          endianness = ".le";
+          break;
+      };
+      return npy_prefix + lts + endianness + ".npy";
     }
 
     TEST(xnpy, load)