Doctoral Inspirations
Monday, September 17th, 2007While reading my Gmail yesterday, I saw a sponsored link titled “The PHP Doctor“. Being a self-proclaimed PHP expert myself, I was interested to see exactly how good this PHP Doctor is. He has a blog–a PHP tips and tricks blog. The first post was about functions, and their use in writing modular code. Although the post used a solid example of functions, I couldn’t help but notice a few sloppy performance issues. The following are tips that I have created after reading that post, and the second post on the page.
- Where possible, do not use functions in the entrance condition for loops. Consider the following example: (From The PHP Doctor*)
for( $x = 0 ; $x < strlen( $InString ); $x++ ) {
if (strstr( $OKChars , $InString[$x] ) ) $OutString .= $InString[$x];
}
Note that for every iteration of that loop, the valuestrlen( $InString )remains the same. However, on each iteration of the loop, the function is run. To avoid running this function each iteration, the value should be assigned to a variable before the first iteration:
for ( $x = 0,$c = strlen( $InString ); $x < $c; $x++) {
if ( strstr( $OKChars , $InString[$x] ) ) $OutString .= $InString[$x];
}
++$i,$i++,$i += 1, and$i = $i + 1all have the same basic effect, but they are indeed different. Using using $i++ or ++$i is faster than using$i += 1 or $i = $i + 1. For those who don’t remember, $i++ and ++$i are respectively, the post increment and the pre increment operators. The difference between the two is that pre increment increments $i, then returns the incremented value, whereas post increment returns the value of $i, then increments $i.- Although PHP doesn’t really care, try to avoid implicitly casting numerical types to strings when it is not necessary. Consider a function that takes a numer, $Number, and rounds it to the nearest hundredth. (Note: this can be done via PHP’s round function:
round($Number,2)). Here is an example from The PHP Doctor*:
function roundToTwo( $Number ) {
//pow(10, -3) = .001
$Number += pow( 10 , -3 ); //Make sure the thousandths place is populated
$Number = round( $Number * pow( 10 , 2 ) ) / pow( 10 , 2 );
//Make sure the thousandths place is populated
$Number += pow( 10 , -3 ); //pow() returns float or int (false on error)
//Take the decimal point, and the following two characters.
$Number = substr( $Number , 0 , strpos( $Number , '.' ) + 3 );
return $Number;
}
Rounding is a mathematical function, but the preceding function relies on properties of strings. One downside of this is performance; another is formatting:roundToTwo()will return a string, and because strings have no concept of significant digits, non-significant digits will be returned. (return value could be something like 123.00) Anyway, with a little more thought, we can find a way to do this without using strings. When round is passed only one argument, it will round the argument to the nearest integer. It follows thatround($Number*100)/100will function the same asroundToTow($Number). But suppose we want to avoid usinground()… Recall that if we are rounding to n decimal places, we round up when the digit in the (n+1)th decimal place is greater than or equal to 5, and down otherwise. Adding 5 to this digit will accomplish this. Thus, we can now use thefloor()function instead ofround():floor($Number*100 + .5)/100. - In the previous example, not the use of pow(x,y) where x and y are constant. For better performance, calculate the value pow(x,y), and use that value in your program. In some cases, this will also lead to more readable code.
This is ensured by standards such as ASCII, ANSI, and ISO. I am using ISO 8859-1; the mac probably isn’t using ISO 8859-1, but it most likely knows how to read it. The character set is specified in the email headers. I can go to a variety of websites, and my browser of choice, Firefox, will have no problem displaying them. This is also due to standards. The w3c, or world wide web consortium was formed in 1994 to oversee open standards for the internet. Without a single organization overseeing standards, different websites would be coded in different languages, and not all browsers would be able to display every website. The internet would be much like the hell described at the beginning of this paragraph.
