Where to save custom functions?

Where in com_easyblog/controllers could I store these functions? If you can point me in the right direction with a tutorial or documentation, I'd greatly appreciate it.

function getfavicon($url){ //get favicon URL from provided URL

	$favicon = '';

	$html = file_get_contents($url);

	$dom = new DOMDocument();

	$dom->loadHTML($html);

	$links = $dom->getElementsByTagName('link');

	for ($i = 0; $i < $links->length; $i++){

		$link = $links->item($i);

		if($link->getAttribute('rel') == 'icon'){

			$favicon = $link->getAttribute('href');

	}

	}

	return $favicon;

}



function strbtw($string, $start, $end){ //get string in between two unique strings

    $string = ' ' . $string;

    $ini = strpos($string, $start);

    if ($ini == 0) return '';

    $ini += strlen($start);

    $len = strpos($string, $end, $ini) - $ini;

    return substr($string, $ini, $len);

}