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Printing EAN-13 Supplement 5 in C# de Complete

Jackson s Rules of Optimization: Rule 1. Don t do it. Rule 2 (for experts only). Don t do it yet that is, not until you have a perfectly clear and unoptimized solution. M. A. Jackson

Use a high-quality design. Make the program right. Make it modular and easily modifiable so that it s easy to work on later. When it s complete and correct, check the performance. If the program lumbers, make it fast and small. Don t optimize until you know you need to. A few years ago I worked on a C++ project that produced graphical outputs to analyze investment data. After my team got the first graph working, testing reported that the program took about 45 minutes to draw the graph, which was clearly not acceptable. We held a team meeting to decide what to do about it. One of the developers became irate and shouted, If we want to have any chance of releasing an acceptable product we ve got to start rewriting the whole code base in assembler right now. I responded that I didn t think so that 4 percent of the code probably accounted for 50 percent or more of the performance bottleneck. It would be best to address that 4 percent toward the end of the project. After a bit more shouting, our manager assigned me to do some initial performance work (which was really a case of Oh no! Please don t throw me into that briar patch! ). As is often the case, a day s work identified a couple of glaring bottlenecks in the code, and a small number of code-tuning changes reduced the drawing time from 45 minutes to less than 30 seconds. Far less than 1 percent of the code accounted for 90 percent of the run time. By the time we released the software months later, several additional code-tuning changes reduced that drawing time to a little more than 1 second.

Modern compiler optimizations might be more powerful than you expect. In the case I described earlier, my compiler did as good a job of optimizing a nested loop as I was able to do by rewriting the code in a supposedly more efficient style. When shopping for a compiler, compare the performance of each compiler on your program. Each compiler has different strengths and weaknesses, and some will be better suited to your program than others. Optimizing compilers are better at optimizing straightforward code than they are at optimizing tricky code. If you do clever things like fooling around with loop indexes, your compiler has a harder time doing its job and your program suffers. See Using Only One Statement per Line in Section 31.5, for an example in which a straightforward approach resulted in compiler-optimized code that was 11 percent faster than comparable tricky code.

With a good optimizing compiler, your code speed can improve 40 percent or more across the board. Many of the techniques described in the next chapter produce gains of only 15-30 percent. Why not just write clear code and let the compiler do the work Here are the results of a few tests to check how much an optimizer speeded up an insertion-sort routine:

Time Without Compiler Optimizations 2.21 2.78 2.43 1.55 1.78 2.77 1.39 2.63 Time with Compiler Optimizations 1.05 1.15 1.25 1.55 1.78 2.77 1.38 2.63 Performance Ratio 2:1 2.5:1 2:1 1:1 1:1 1:1 1:1 1:1

Language C++ compiler 1 C++ compiler 2 C++ compiler 3 C# compiler Visual Basic Java VM 1 Java VM 2 Java VM 3

Time Savings 52% 59% 49% 0% 0% 0% <1% 0%

The only difference between versions of the routine was that compiler optimizations were turned off for the first compile, on for the second. Clearly, some compilers optimize better than others, and some are better without optimizations in the first place. Some JVMs are also clearly better than others. You ll have to check your own compiler, JVM, or both to measure its effect.