define __pure and __const

src/include/compiler.h

 /** Apply standard C calling conventions */
 #define __cdecl __attribute__ (( cdecl , regparm(0) ))
 
+/**
+ * Declare a function as pure - i.e. without side effects
+ */
+#define __pure __attribute__ (( pure ))
+
+/**
+ * Declare a function as const - i.e. it does not access global memory
+ * (including dereferencing pointers passed to it) at all.
+ * Must also not call any non-const functions.
+ */
+#define __const __attribute__ (( const ))
+
 /**
  * Declare a function as used.
  *