Fast dynamic casting

We describe a scheme for implementing dynamic casts suitable for systems where the performance and predictability of performance is essential. A dynamic cast from a base class to a derived class in an objectoriented language can be performed quickly by having the linker assign an integer type ID to each class. A simple integer arithmetic operation verifies whether the cast is legal at run time. The type ID scheme presented uses the modulo function to check that one class derives from another. A 64-bit type ID is sufficient to handle class hierarchies of large size at least nine levels of derivation deep. We also discuss the pointer adjustments required for a C++ dynamic cast. All examples will be drawn from the C++ language. Copyright c © 2005 John Wiley & Sons, Ltd.