Optimization in programming

Optimization is the art of going through a program and making the code more efficient so that it runs faster. Most compilers have a command-line switch that causes them to generate optimized code. This efficiency comes at the cost of compile time; the compiler takes a lot longer to generate code when optimization is turned on.

The other type of optimization occurs when a programmer modifies a program to use a more efficient algorithm. This section discusses this second type of optimization.

How to Optimize:

Here are several optimizing strategies mentioned:

Loop ordering:

Nested loops should be ordered with the simplest loop outermost and the

most complex loops innermost.

Reduction in strength:

This phrase is a fancy way of saying you should use cheap operations instead

of expensive ones. The table at the top-right hand side explains the relative cost of each operation in a descending order.

Powers of 2:

Use a power of 2 when doing integer multiply or divide. Most compilers

substitute a shift for the operation.

Pointers:

Using pointers is faster than indexing an array. Pointers are, however, more

tricky to use.

Macros:

Using a macro eliminates the overhead associated with a function call. It also

makes the code bigger and a little more difficult to debug.

Source: Practical C Programming, Third Edition - O'Reilly Media