FreeTDM: Add ftdm_offset_of() and ftdm_container_of() macros.

Might as well import these too...

ftdm_offset_of() - Get offset of member in structure.

ftdm_container_of() - Get pointer to enclosing structure from pointer to structure member.

Signed-off-by: Stefan Knoblich <stkn@openisdn.net>

diff --git a/libs/freetdm/src/include/ftdm_os.h b/libs/freetdm/src/include/ftdm_os.h
index f8681111b6430e705889c94fe837f757b434898d..39afec94be3be0565ca3ed19648f9de0dbc7a8d9 100644 (file)
--- a/libs/freetdm/src/include/ftdm_os.h
+++ b/libs/freetdm/src/include/ftdm_os.h
@@ -87,6 +87,45 @@ typedef uint64_t ftdm_time_t;
 /*! \brief Get value that is in range [vmin,vmax] */
 #define ftdm_clamp(val,vmin,vmax) ftdm_max(vmin,ftdm_min(val,vmax))
 
+/*!
+ * \brief Get offset of member in structure
+ * \param[in]  type    Type of struct
+ * \param[in]  member  Name of struct member
+ * \code
+ *     struct a {
+ *             int foo;
+ *             int bar;
+ *     };
+ *
+ *     int offset_a_bar = ftdm_offset_of(struct a, bar); // 4 byte offset
+ * \endcode
+ */
+#define ftdm_offset_of(type,member) (uintptr_t)&(((type *)0)->member)
+
+/*!
+ * \brief Get pointer to enclosing structrure from pointer to embedded member
+ * \param[in]  ptr     Pointer to embedded member
+ * \param[in]  type    Type of parent/container structure
+ * \param[in]  member  Name of embedded member in parent/container struct
+ * \code
+ *     struct engine {
+ *             int nr_cyl;
+ *     };
+ *
+ *     struct car {
+ *             char model[10];
+ *             struct engine eng;      // struct engine embedded in car(!)
+ *     };
+ *
+ *     int somefunc(struct engine *e) {
+ *             struct car *c = ftdm_container_of(e, struct car, eng);
+ *
+ *             ... do something with car ...
+ *     }
+ * \endcode
+ */
+#define ftdm_container_of(ptr,type,member) (type *)((uintptr_t)(ptr) - ftdm_offset_of(type, member))
+
 
 /*! \brief The memory handler. 
     Do not use directly this variable, use the memory macros and ftdm_global_set_memory_handler to override */