This package is copyright protected under the GPL terms, which means that it is what is called 'free software'. (see COPYING)
Defining the macro RPTR_DEBUG activates a runtime check for null pointer dereferencing. On error an assertion fails and the program aborts. Together with a standard debugger this will hopefully help in finding your bugs easily.
Beware that the runtime checks will give an efficiency penalty.
Also beware that compiling only some files with RPTR_DEBUG may sometimes produce strange results because inlined functions may be defined differently in different object files. It is recommended not to link together files compiled with different RPTR_DEBUG macro settings.