PHP n-gram Algorithm

function getNgrams($match, $n=3)
		{
			$ngrams = array();
			$len = strlen($match);
			for ($i = 0; $i < $len; $i++)
			{
				if ($i > ($n - 2))
				{
					$ng = '';
					for($j = $n - 1; $j >= 0; $j--)
					{
						$ng .= $match[$i - $j];
					}
					$ngrams[] = $ng;
				}
			}
			return $ngrams;
		}