BrainF*ck Interpreter

<?php
class BF
{
    /*
     *
     * Developer(s): Kai (Tux.)
     * Description: A BrainF*ck interpreter
     *
     * USAGE:
     * $bf = new BF();
     * echo $bf->interpret('codeHere', 'optionalInputHere');
     *
     */

    protected $pointer = 0, $validChars = array('>','<','.',',','+','-','[',']');
    protected $cell = array(), $output = '', $input = '', $inputPointer = 0;

    public function interpret( $code, $input = '' ) {
        $preparedCode = $this->prepare($code); // strip invalid characters and break into sections
        $this->initializeCells(); // initialize cells to 0 for 30,000 cells
        $this->input = $input;
        #return print_r($code);
        foreach($preparedCode as $line) { //loop threw the sections
            if($line[0]) { // is a loop
                $safeGuard = 0;
                // Loop until the it lands on a cell that is zeroed out.
                //Only starts if current cell is not 0
                while($this->cell[$this->pointer]) {
                    // if has looped more that 10,000 times then exit script and throw an error
                    if($safeGuard > 10000) {
                        die(print("Error in section:<br />\n'[{$line[1]}]'"));
                    }
                    // loop threw and interpret each character in the section
                    foreach(str_split($line[1]) as $char) {
                        $this->interpretChar($char);
                        $safeGuard++;
                    }
                }
            } else { // not a loop
                // loop threw and interpret each character in the section
                foreach(str_split($line[1]) as $char) {
                    $this->interpretChar($char);
                }
            }
        }
        return $this->output;
    }

    protected function initializeCells() {
        for($i=0;$i<=30000;$i++) {
            $this->cell[$i] = 0;
        }
    }

    protected function prepare( $code ) {
        // some needed functions
        $inBrackets = false;
        $buffer = '';
        $array = array();
        // strip invalid characters
        foreach(str_split($code) as $char) {
            if(!in_array($char, $this->validChars, true)) {
                $code = str_replace($char, '', $code);
            }
        }
        //split into sections of loops and non loops
        foreach(str_split($code) as $char) {
            if($inBrackets) {
                if($char === ']') {
                    $inBrackets = false;
                    $array[] = array(true, $buffer);
                    $buffer = '';
                } else {
                    $buffer .= $char;
                }
            } else {
                if($char === '[') {
                    $inBrackets = true;
                    $array[] = array(false, $buffer);
                    $buffer = '';
                } else {
                    $buffer .= $char;
                }
            }
        }
        //get the last lingering section if there is one
        if($buffer !== '') {
            $array[] = array(false, $buffer);
            $buffer = '';
        }
        //return the processed code
        return $array;
    }

    protected function interpretChar( $char ) {
        switch($char) {
            case '>':
                return $this->cellForward();
            case '<':
                return $this->cellBackward();
            case '.':
                return $this->cellPrint();
            case ',':
                return $this->cellStore();
            case '+':
                return $this->cellIncriment();
            case '-':
                return $this->cellDecriment();
        }
    }

    protected function cellForward() {
        if($this->pointer !== 30000) {
            $this->pointer++;
        } else {
            $this->pointer = 0;
        }
    }

    protected function cellBackward() {
        if($this->pointer !== 0) {
            $this->pointer--;
        } else {
            $this->pointer = 30000;
        }
    }

    protected function cellPrint() {
        $this->output .= chr($this->cell[$this->pointer]);
    }

    protected function cellStore() {
        if(isset($this->input[$this->inputPointer])) {
            $this->cell[$this->pointer] = ord($this->input[$this->inputPointer]);
            $this->inputPointer++;
        }
    }

    protected function cellIncriment() {
        $this->cell[$this->pointer]++;
    }

    protected function cellDecriment() {
        if($this->cell[$this->pointer] !== 0) {
            $this->cell[$this->pointer]--;
        }
    }
}
?>