Editing Program optimization (section)

==Strength reduction==
Computational tasks can be performed in several different ways with varying efficiency. A more efficient version with equivalent functionality is known as a [[strength reduction]]. For example, consider the following [[C (programming language)|C]] code snippet whose intention is to obtain the sum of all integers from 1 to {{var|N}}:

<syntaxhighlight lang="c">
int i, sum = 0;
for (i = 1; i <= N; ++i) {
  sum += i;
}
printf("sum: %d\n", sum);
</syntaxhighlight>

This code can (assuming no [[arithmetic overflow]]) be rewritten using a mathematical formula like:

<syntaxhighlight lang="c">
int sum = N * (1 + N) / 2;
printf("sum: %d\n", sum);
</syntaxhighlight>

The optimization, sometimes performed automatically by an optimizing compiler, is to select a method ([[algorithm]]) that is more computationally efficient, while retaining the same functionality. See [[algorithmic efficiency]] for a discussion of some of these techniques. However, a significant improvement in performance can often be achieved by removing extraneous functionality.

Optimization is not always an obvious or intuitive process. In the example above, the "optimized" version might actually be slower than the original version if {{var|N}} were sufficiently small and the particular hardware happens to be much faster at performing addition and [[Loop (computing)#Loops|loop]]ing operations than multiplication and division.