PHP で指定された週番号から曜日を効率的に抽出する方法は?

<code class="php"><?php
$week_number = 40;
$year = 2008;
for ($day = 1; $day <= 7; $day++) {
    echo date('m/d/Y', strtotime($year . 'W' . $week_number . $day)) . "\n";
}
?></code>

<code class="php"><?php
function week_from_monday($date) {
    list($day, $month, $year) = explode('-', $date);
    $wkday = date('l', mktime(0, 0, 0, $month, $day, $year));
    switch ($wkday) {
        case 'Monday': $numDaysToMon = 0; break;
        case 'Tuesday': $numDaysToMon = 1; break;
        case 'Wednesday': $numDaysToMon = 2; break;
        case 'Thursday': $numDaysToMon = 3; break;
        case 'Friday': $numDaysToMon = 4; break;
        case 'Saturday': $numDaysToMon = 5; break;
        case 'Sunday': $numDaysToMon = 6; break;
    }

    $monday = mktime(0, 0, 0, $month, $day - $numDaysToMon, $year);
    $seconds_in_a_day = 86400;
    for ($i = 0; $i < 7; $i++) {
        $dates[$i] = date('Y-m-d', $monday + ($seconds_in_a_day * $i));
    }

    return $dates;
}

$date = '07-10-2008';
$dates = week_from_monday($date);
print_r($dates);
?></code>