cmMath.c, cmThread.c : Replaced type casting with use of unions to do type conversion in byte swap and CAS functions.

This was required to address a strict-aliasing violation in the release build.

cmMath.c

 
 //=================================================================
 // Floating point byte swapping
+
+// Unions used to type-pun the swapping functions and thereby 
+// avoid strict aliasing problems with -O2.  Using unions for 
+// this purpose is apparently legal under C99 but not C++.
+
+typedef union
+{
+  unsigned u;
+  float    f;
+} _cmMathU_t;
+
+typedef union
+{
+  unsigned long long u;
+  double    f;
+} _cmMathUL_t;
+
 unsigned           cmFfSwapFloatToUInt( float v )
 {
   assert( sizeof(float) == sizeof(unsigned));
-  return cmSwap32(*(unsigned*)&v);
+  _cmMathU_t u;
+  u.f=v;
+  return cmSwap32(u.u);
 }
 
 float              cmFfSwapUIntToFloat( unsigned v )
 {
   assert( sizeof(float) == sizeof(unsigned));
-  v = cmSwap32(v);
-  return *((float*)&v);
+  _cmMathU_t u;
+
+  u.u = cmSwap32(v);
+  return u.f;
 }
 
 unsigned long long cmFfSwapDoubleToULLong( double v )
 {
   assert( sizeof(double) == sizeof(unsigned long long));
-  return cmSwap64(*(unsigned long long*)&v);
+  _cmMathUL_t u;
+  u.f = v;
+  return cmSwap64(u.u);
 }
 
 double             cmFfSwapULLongToDouble( unsigned long long v )
 {
   assert( sizeof(double) == sizeof(unsigned long long));
-  v = cmSwap64(v);
-  return *((double*)&v);
+  _cmMathUL_t u;
+  u.u = cmSwap64(v);
+  return u.f;
 }

cmThread.c

 #endif
 
 #ifdef OS_LINUX
-  return  __sync_bool_compare_and_swap((unsigned*)addr, *(unsigned*)(&old),*(unsigned*)(&new)); 
+  // If we use pointer aliasing to pun the pointer types then it will violate the
+  // strict pointer aliasing rules used by -O2. Instead we use this union
+  // punning scheme which in theory should always work in C99 (although no C++).
+
+  typedef union 
+  {
+    unsigned* up;
+    float*    fp;
+  } u;
+
+  u u0,u1;
+  u0.fp = &old;
+  u1.fp = &new;
+
+  return  __sync_bool_compare_and_swap((unsigned*)addr,*u0.up,*u1.up); 
 #endif
 }