Jon's Cache-Control header parser

CacheControlParser.php

<?php
function parseValue($value)
{
    $directives = array();
    $lastPosition = 0;
    $array = str_split($value);
    while (false !== ($token = tokenizer($value, $array, ', ', $lastPosition))) {
        $directive = explode('=', trim($token));
        if (false === $directive) {
            throw new Exception('Invalid header line for Cache-Control string: "' . $value . '"');
        }
        if (preg_match('/^[^a-zA-Z]{1,1}/', $directive[0])) {
            throw new Exception('Invalid Cache-Control directive: "' . $token . '"');
        }
        $directives[$directive[0]] = true;
        if (isset($directive[1])) {
            if (!preg_match('/^"([^"]*)"|([^ \t",;]*)$/', $directive[1])) {
                throw new Exception('Invalid Cache-Control directive: "' . $token . '"');
            }
            $directives[$directive[0]] = trim($directive[1], '"');
        }
    }
    return $directives;
}

function tokenizer($string, $array, $sep, &$lastPosition)
{
    $quoted = false;
    $startPosition = $lastPosition;
    $length = count($array);
    if ($lastPosition > $length) {
        return false;
    }
    for ($lastPosition; $lastPosition < $length; $lastPosition++) {
        if (!$quoted) {
            if ('"' == $array[$lastPosition]) {
                $quoted = true;
            } elseif (false !== strpos($sep, $array[$lastPosition])) {
                if ($startPosition == $lastPosition) {
                    $startPosition = $lastPosition = $lastPosition++;
                    continue;
                } else {
                    $lastPosition++;
                    break;
                }
            }
        } else {
            if ('"' == $array[$lastPosition]) {
                $quoted = false;
            }
        }
    }
    return substr($string, $startPosition, $lastPosition - $startPosition);
}

try {
    var_dump(parseValue('no-store& private=test, no-cache="a,b,c"'));
} catch (Exception $e) {
    var_dump($e->getMessage());
}

$start = microtime(true);
for ($i=0; $i<10000; $i++) {
    parseValue('no-store, private=test, no-cache="a,b,c"');
}
var_dump(microtime(true) - $start);