consolidated implementation of BigEndian

- works for any type size
- checks that we are dealing with numbers
- remove pointers in favor of more elegant c++ unions

src/output/vtk.hpp

@@ -21,25 +21,18 @@
 #include "idefix.hpp"
 #include "input.hpp"
 #include "dataBlock.hpp"
+#include "bigEndian.hpp"
 #include "scalarField.hpp"
 
+
 // Forward class declaration
 class Output;
 class DataBlock;
 
 
 class BaseVtk {
- private:
-  // Endianness swaping function and variable
-  bool shouldSwapEndian {true};
-
  protected:
   BaseVtk() {
-    // Test endianness
-    int tmp1 = 1;
-    unsigned char *tmp2 = (unsigned char *) &tmp1;
-    if (*tmp2 == 0)
-      this->shouldSwapEndian = false;
     // Initialise the root tag (used for MPI non-collective I/Os)
     this->isRoot = idfx::prank == 0;
   }
@@ -68,25 +61,9 @@ class BaseVtk {
   // DataBlock parent
   DataBlock *data;
 
-  /* ****************************************************************************/
-  /** Determines if the machine is little-endian.  If so,
-    it will force the data to be big-endian.
-  @param in_number floating point number to be converted in big endian */
-  /* *************************************************************************** */
+  // BigEndian conversion
+  BigEndian BigEndian;
 
-  template <typename T>
-  T BigEndian(T in_number) {
-    if (shouldSwapEndian) {
-      unsigned char *bytes = (unsigned char*) &in_number;
-      unsigned char tmp = bytes[0];
-      bytes[0] = bytes[3];
-      bytes[3] = tmp;
-      tmp = bytes[1];
-      bytes[1] = bytes[2];
-      bytes[2] = tmp;
-    }
-    return(in_number);
-  }
 
   void WriteHeaderString(const char* header, IdfxFileHandler fvtk) {
   #ifdef WITH_MPI

src/utils/CMakeLists.txt

@@ -1,6 +1,7 @@
 add_subdirectory(iterativesolver)
 
 target_sources(idefix
+  PUBLIC ${CMAKE_CURRENT_LIST_DIR}/bigEndian.hpp
   PUBLIC ${CMAKE_CURRENT_LIST_DIR}/dumpImage.cpp
   PUBLIC ${CMAKE_CURRENT_LIST_DIR}/dumpImage.hpp
   PUBLIC ${CMAKE_CURRENT_LIST_DIR}/lookupTable.hpp

src/utils/bigEndian.hpp

@@ -0,0 +1,63 @@
+// ***********************************************************************************
+// Idefix MHD astrophysical code
+// Copyright(C) Geoffroy R. J. Lesur <geoffroy.lesur@univ-grenoble-alpes.fr>
+// and other code contributors
+// Licensed under CeCILL 2.1 License, see COPYING for more information
+// ***********************************************************************************
+
+#ifndef UTILS_BIGENDIAN_HPP_
+#define UTILS_BIGENDIAN_HPP_
+
+#include <cstddef>
+#include <type_traits>
+#include "idefix.hpp"
+
+/* ****************************************************************************/
+/** Determines if the machine is little-endian.  If so,
+  it will force the data to be big-endian.
+@param in_number floating point number to be converted in big endian */
+/* *************************************************************************** */
+
+class BigEndian {
+ public:
+  BigEndian() {
+    // Test endianness
+    union {
+        uint32_t i;
+        char c[4];
+    } bint = {0x01020304};
+
+    if(bint.c[0] == 1)
+      this->shouldSwapEndian = false;
+    else
+      this->shouldSwapEndian = true;
+  }
+
+  // Swap when needed
+  template <class T>
+  T operator() (T in_number) {
+    static_assert(std::is_arithmetic_v<T> == true);
+    T out_number;
+    if (this->shouldSwapEndian) {
+      constexpr int size = sizeof(T);
+      union {
+        T u;
+        unsigned char byte[size];
+      } in, out;
+      in.u = in_number;
+      for(int n = 0 ; n < size ; n++) {
+        out.byte[size-n-1] = in.byte[n];
+      }
+      out_number = out.u;
+    } else {
+      out_number = in_number;
+    }
+    return(out_number);
+  }
+
+ private:
+  // Endianness swaping flag
+  bool shouldSwapEndian;
+};
+
+#endif // UTILS_BIGENDIAN_HPP_