PhD Thesis - staffweb - University of Greenwich

APPENDIX 2 : Journal Paper "Case Study : An Incremental Approach to Re-Engineeringa Legacy FORTRAN C.F.D. Code in C++", Ewer J., Knight B. and Cowell D.,Advances in Engineering Software, Vol. 22, pp 153-168, 1995Figure 17 :Comparative values of vertical velocity for natural convection.Appraisal of the re-engineering strategy:The observed 50 percent performance overhead of the C++ implementation, on theSun system, was probably the more realistic of the timing comparisons because both theSun FORTRAN and Sun C++ compilers generate compatible binary code and have identicalcompilation options. Similar overheads have been reported in other numerical codetranslations and are mostly due to the introduction of more layers of function calls at a lowlevel within the C++ code. This was particularly true of the case-study code implementationwhere two and sometimes three levels of function calls have been introduced. It is generallyaccepted that the introduction of a high degree of object-orientation and code clarity usuallyaffect the performance adversely. Higher overheads have been recorded in C++implementations where inheritance and virtual classes have been used.The consistency between the simulation solutions of the legacy and re-engineeredsystems indicates that the codes exhibit highly compatible behaviour. This was coupledwith an easily comprehensible implementation that was largely self documenting. Theenhanced monitoring and debugging facilities of the re-engineered system have been usedin subsequent research to good effect. These factors indicate that the re-engineeringobjectives have largely been met during this case study.One of the major benefits of the re-engineering approach adopted in this researchwas that the newest version of the code could be compiled and tested after each incrementalstage. In fact the testing was generally done after every major global change or after a singleAppendix 11.2 Page 142-24 24