Fix alignment issues in CELX routines (Closes: #263)

src/celestia/celx_rotation.cpp

@@ -12,14 +12,15 @@
 #include "celx.h"
 #include "celx_internal.h"
 #include "celx_vector.h"
+#include <celutil/align.h>
 
 using namespace Eigen;
 
 int rotation_new(lua_State* l, const Quaterniond& qd)
 {
     CelxLua celx(l);
-    auto q = reinterpret_cast<Quaterniond*>(lua_newuserdata(l, sizeof(Quaterniond)));
-    memcpy(q, &qd, sizeof(Quaterniond));
+    auto q = reinterpret_cast<Quaterniond*>(lua_newuserdata(l, aligned_sizeof<Quaterniond>()));
+    *aligned_addr(q) = qd;
     celx.setClass(Celx_Rotation);
 
     return 1;
@@ -28,8 +29,9 @@ int rotation_new(lua_State* l, const Quaterniond& qd)
 Quaterniond* to_rotation(lua_State* l, int index)
 {
     CelxLua celx(l);
+    auto q = reinterpret_cast<Quaterniond*>(celx.checkUserData(index, Celx_Rotation));
 
-    return static_cast<Quaterniond*>(celx.checkUserData(index, Celx_Rotation));
+    return aligned_addr(q);
 }
 
 static Quaterniond* this_rotation(lua_State* l)

src/celestia/celx_vector.cpp

@@ -12,15 +12,17 @@
 #include "celx.h"
 #include "celx_internal.h"
 #include "celx_vector.h"
+#include <celutil/align.h>
 #include <Eigen/Geometry>
+
 using namespace Eigen;
 
 int vector_new(lua_State* l, const Vector3d& v)
 {
     CelxLua celx(l);
 
-    auto v3 = reinterpret_cast<Vector3d*>(lua_newuserdata(l, sizeof(Vector3d)));
-    *v3 = v;
+    auto v3 = reinterpret_cast<Vector3d*>(lua_newuserdata(l, aligned_sizeof<Vector3d>()));
+    *aligned_addr(v3) = v;
     celx.setClass(Celx_Vec3);
 
     return 1;
@@ -29,8 +31,9 @@ int vector_new(lua_State* l, const Vector3d& v)
 Vector3d* to_vector(lua_State* l, int index)
 {
     CelxLua celx(l);
+    auto v = reinterpret_cast<Vector3d*>(celx.checkUserData(index, Celx_Vec3));
 
-    return static_cast<Vector3d*>(celx.checkUserData(index, Celx_Vec3));
+    return aligned_addr(v);
 }
 
 static Vector3d* this_vector(lua_State* l)

src/celutil/align.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include <type_traits>
+
+/*! Returns aligned position for type T inside memory region.
+ *  Designed for usage with functions which allocate unalligned
+ *  memory regions.
+ */
+template<typename T> T* aligned_addr(T* addr)
+{
+    size_t align = std::alignment_of<T>::value;
+    return (T*) (((size_t(addr) - 1) / align + 1) * align);
+};
+
+template<typename T> T* aligned_addr(T* addr, size_t align)
+{
+    return (T*) (((size_t(addr) - 1) / align + 1) * align);
+};
+
+/*! Returns size large enough so an object of type T can be placed
+ *  inside allocated unalligned memory region with its address aligned.
+ */
+template<typename T> size_t aligned_sizeof()
+{
+    return sizeof(T) + std::alignment_of<T>::value - 1;
+};