c# generating barcode Language C# Java Visual Basic in C#.NET

Draw GS1 - 13 in C#.NET Language C# Java Visual Basic

These results defy any logical explanation. In one of the languages, case is dramatically superior to if-then-else, and in another, if-then-else is dramatically superior to case. In the third language, the difference is relatively small. You might think that because C# and Java share similar syntax for case statements, their results would be similar, but in fact their results are opposite each other. This example clearly illustrates the difficulty of performing any sort of rule of thumb or logic to code tuning there is simply no reliable substitute for measuring results.

In some circumstances, a table lookup may be quicker than traversing a complicated chain of logic. The point of a complicated chain is usually to categorize something and then to take an action based on its category. As an abstract example, suppose you want to assign a category number to something based on which of Groups A, B, and C it falls into:

1 2 0

1 1 2 3

Here s an example of the complicated logic chain that assigns the category numbers:

if ( ( a && !c ) || ( a && b && c ) ) { category = 1; } else if ( ( b && !a ) || ( a && c && !b ) ) { category = 2; } else if ( c && !a && !b ) { category = 3; } else { category = 0; }

You can replace this test with a more modifiable and higher-performance lookup table. Here s how:

2 This table definition is somewhat difficult to understand. Any commenting you can do to make table definitions readable helps.

static int categoryTable[ 2 ][ 2 ][ 2 ] = { // !b!c 0, 1, }; ... category = categoryTable[ a ][ b ][ c ]; !bc 3, 2, b!c 2, 1, bc 2, 1 // // !a a

Although the definition of the table is hard to read, if it s well documented it won t be any harder to read than the code for the complicated chain of logic was. If the definition changes, the table will be much easier to maintain than the earlier logic would have been. Here are the performance results:

Time Savings 33% 50%

Performance Ratio 1.5:1 2:1

One of my former roommates was a great procrastinator. He justified his laziness by saying that many of the things people feel rushed to do simply don t need to be done. If he waited long enough, he claimed, the things that weren t important would be procrastinated into oblivion, and he wouldn t waste his time doing them. Lazy evaluation is based on the principle my roommate used. If a program uses lazy evaluation, it avoids doing any work until the work is needed. Lazy evaluation is similar to just-in-time strategies that do the work closest to when it s needed. Suppose, for example, that your program contains a table of 5000 values, generates the whole table at startup time, and then uses it as the program executes. If the program uses only a small percentage of the entries in the table, it might make more sense to compute them as they re needed rather than all at once. Once an entry is computed, it can still be stored for future reference ( cached ).

Because loops are executed many times, the hot spots in a program are often inside loops. The techniques in this section make the loop itself faster.

Switching refers to making a decision inside a loop every time it s executed. If the decision doesn t change while the loop is executing, you can unswitch the loop by making the decision outside the loop. Usually this requires turning the loop inside out, putting loops inside the conditional rather than putting the conditional inside the loop. Here s an example of a loop before unswitching: