Function calls can be very expensive in terms of CPU usage. Try to reduce the use of them inside loops. The two primary ways to do this are:

• Eliminate repeated calls to the same function with the same parameters
• Inline small, simple functions

I'll look at inlining separately in Optimizing loops: inline function calls.

At first you may think, "Why would anyone repeatedly call the same function with the same parameters?" It's a reasonable question, but consider the following very common type of loop construct:

for ( $i=0; $i<count($myArray); ++$i )
   // do something

Although it appears innocent enough, that call to count($myArray) is made once every iteration. In any such loop, provided it doesn't add or remove elements from $myArray, the size of the array and hence the value returned by count($myArray) remains constant. You can write it more efficiently as follows:

$arraySize = count($myArray);
for ( $i=0; $i<$arraySize; ++$i )
   // do something

Notice how the call to count($myArray) is made just once now rather than once per iteration in the initial code example. This second approach does create another, temporary variable, but it gives better overall performance.