Split long string efficiently?

I need a way to split a long string efficiently into smaller chunks into an array, does anyone know the best way?

Example:


$string = "THIS IS A SUPER LONG STRING THAT I NEED TO SPLIT INTO SMALLER CHUNKS OF ABOUT THE SAME LENGTH, IS THERE ANYWAY TO DO THIS?";

$string = magic_function($string);
echo $string[0];
echo $string[1];

of course replacing magic_function with a real function!