Avoid clang/32 optimization affecting IEEE endian detection

This turns the detection code into a c++ file, moves the
structure to a global one and adds volatile specifiers.
This should hopefully prevent any standard-adhering
compiler from touching the data.

Change-Id: I6f4b86ddf6b0567655466e0877bb1ba39a45ce4e

diff --git a/cmake/TestFloatFormat.c b/cmake/TestFloatFormat.c
deleted file mode 100644 (file)
index d0676d5..0000000
--- a/cmake/TestFloatFormat.c
+++ /dev/null
@@ -1,32 +0,0 @@
-int
-main()
-{
-  /* Check that a double is 8 bytes - compilation dies if it isnt */
-  extern char xyz [sizeof(double) == 8 ? 1 : -1];
-  int i;
-  double d;
-
-  double abc [10] = {
-    /* Zero-terminated strings encoded as floating-point numbers */
-    /* "GROMACSX" in ascii    */
-    (double)  3.80279098314984902657e+35 , (double) 0.0,
-    /* "GROMACSX" in ebcdic   */
-    (double) -1.37384666579378297437e+38 , (double) 0.0,
-    /* "D__float" (vax)       */
-    (double)  3.53802595280598432000e+18 , (double) 0.0,
-    /* "IBMHEXFP" s390/ascii  */
-    (double)  1.77977764695171661377e+10 , (double) 0.0,
-    /* "IBMHEXFP" s390/ebcdic */
-    (double) -5.22995989424860458374e+10 , (double) 0.0,
-  };
-
-  /* Make sure some compilers do not optimize away the entire structure
-   * with floating-point data by using it to produce a return value.
-   */
-  for(i=0,d=0;i<10;i++)
-  {
-    d+=abc[i];
-  }
-
-  return (d==12345.0);
-}

diff --git a/cmake/TestFloatFormat.cpp b/cmake/TestFloatFormat.cpp
new file mode 100644 (file)
index 0000000..ea661dc
--- /dev/null
+++ b/cmake/TestFloatFormat.cpp
@@ -0,0 +1,67 @@
+/*
+ * This file is part of the GROMACS molecular simulation package.
+ *
+ * Copyright (c) 2014, by the GROMACS development team, led by
+ * Mark Abraham, David van der Spoel, Berk Hess, and Erik Lindahl,
+ * and including many others, as listed in the AUTHORS file in the
+ * top-level source directory and at http://www.gromacs.org.
+ *
+ * GROMACS is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public License
+ * as published by the Free Software Foundation; either version 2.1
+ * of the License, or (at your option) any later version.
+ *
+ * GROMACS is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with GROMACS; if not, see
+ * http://www.gnu.org/licenses, or write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA.
+ *
+ * If you want to redistribute modifications to GROMACS, please
+ * consider that scientific software is very special. Version
+ * control is crucial - bugs must be traceable. We will be happy to
+ * consider code for inclusion in the official distribution, but
+ * derived work must not be called official GROMACS. Details are found
+ * in the README & COPYING files - if they are missing, get the
+ * official version at http://www.gromacs.org.
+ *
+ * To help us fund GROMACS development, we humbly ask that you cite
+ * the research papers on the package. Check out http://www.gromacs.org.
+ */
+#include <stdio.h>
+
+volatile const double abc [10] = {
+    /* Zero-terminated strings encoded as floating-point numbers */
+    /* "GROMACSX" in ascii    */
+    (double)  3.80279098314984902657e+35, (double) 0.0,
+    /* "GROMACSX" in ebcdic   */
+    (double) -1.37384666579378297437e+38, (double) 0.0,
+    /* "D__float" (vax)       */
+    (double)  3.53802595280598432000e+18, (double) 0.0,
+    /* "IBMHEXFP" s390/ascii  */
+    (double)  1.77977764695171661377e+10, (double) 0.0,
+    /* "IBMHEXFP" s390/ebcdic */
+    (double) -5.22995989424860458374e+10, (double) 0.0,
+};
+
+int
+main()
+{
+    /* Check that a double is 8 bytes - compilation dies if it isnt */
+    extern char xyz [sizeof(double) == 8 ? 1 : -1];
+    int         i;
+    double      d;
+
+    /* Make sure some compilers do not optimize away the entire structure
+     * with floating-point data by using it to produce a return value.
+     */
+    for (i = 0, d = 0; i < 10; i++)
+    {
+        d += abc[i];
+    }
+    return (d == 12345.0);
+}

diff --git a/cmake/gmxTestFloatFormat.cmake b/cmake/gmxTestFloatFormat.cmake
index e20c49d8c4f8a37946f69345311a3437f40ad945..91f6d453035175870fbfe08d2e7f6f7621ff0943 100644 (file)
--- a/cmake/gmxTestFloatFormat.cmake
+++ b/cmake/gmxTestFloatFormat.cmake
@@ -50,7 +50,7 @@ MACRO(GMX_TEST_FLOAT_FORMAT FP_IEEE754 FP_BIG_ENDIAN_BYTE FP_BIG_ENDIAN_WORD)
         MESSAGE(STATUS "Checking floating point format")
 
         TRY_COMPILE(HAVE_${FP_IEEE754} "${CMAKE_BINARY_DIR}"    
-                    "${CMAKE_SOURCE_DIR}/cmake/TestFloatFormat.c"
+                    "${CMAKE_SOURCE_DIR}/cmake/TestFloatFormat.cpp"
                     COPY_FILE "${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/TestFloatFormat.bin")  
 
         if(HAVE_${FP_IEEE754})