CSeoPageChecker::_GetContrast

function _GetContrast($word)
{
	if (null == $this->__index_total_len)
		$this->__index_total_len = array_sum($this->__index['TOTAL']);

	$logDocLength = log($this->__index_total_len < 20 ? 20 : $this->__index_total_len);

	$count = intval($this->__index['TOTAL'][$word]);

	return log($count+1)/$logDocLength;
}