function calendar_week_mod_me($num) {
$base = 7;
return ($num - $base*floor($num/$base));
}

add_filter('get_calendar', 'my_calendar');

function my_calendar($initial = true, $echo = true) {
global $wpdb, $m, $monthnum, $year, $wp_locale, $posts;

// week_begins = 0 stands for Sunday
$week_begins = (int) get_option( 'start_of_week' );
$ts = current_time( 'timestamp' );

// Let's figure out when we are
if ( ! empty( $monthnum ) && ! empty( $year ) ) {
$thismonth = zeroise( intval( $monthnum ), 2 );
$thisyear = (int) $year;
} elseif ( ! empty( $w ) ) {
// We need to get the month from MySQL
$thisyear = (int) substr( $m, 0, 4 );
//it seems MySQL's weeks disagree with PHP's
$d = ( ( $w - 1 ) * 7 ) + 6;
$thismonth = $wpdb->get_var("SELECT DATE_FORMAT((DATE_ADD('{$thisyear}0101', INTERVAL $d DAY) ), '%m')");
} elseif ( ! empty( $m ) ) {
$thisyear = (int) substr( $m, 0, 4 );
if ( strlen( $m ) < 6 ) {
$thismonth = '01';
} else {
$thismonth = zeroise( (int) substr( $m, 4, 2 ), 2 );
}
} else {
$thisyear = gmdate( 'Y', $ts );
$thismonth = gmdate( 'm', $ts );
}

$unixmonth = mktime( 0, 0 , 0, $thismonth, 1, $thisyear );
$last_day = date( 't', $unixmonth );

// Get the next and previous month and year with at least one post
$previous = $wpdb->get_row("SELECT MONTH(post_date) AS month, YEAR(post_date) AS year
FROM $wpdb->posts
WHERE post_date < '$thisyear-$thismonth-01'
AND post_type = 'post' AND post_status = 'publish'
ORDER BY post_date DESC
LIMIT 1");
$next = $wpdb->get_row("SELECT MONTH(post_date) AS month, YEAR(post_date) AS year
FROM $wpdb->posts
WHERE post_date > '$thisyear-$thismonth-{$last_day} 23:59:59'
AND post_type = 'post' AND post_status = 'publish'
ORDER BY post_date ASC
LIMIT 1");

/* translators: Calendar caption: 1: month name, 2: 4-digit year */
$calendar_caption = _x('%1$s %2$s', 'calendar caption');
$calendar_output = '<table id="wp-calendar">
<caption>' . sprintf(
$calendar_caption,
$wp_locale->get_month( $thismonth ),
date( 'Y', $unixmonth )
) . '</caption>
<thead>
<tr>';

$myweek = array();

for ( $wdcount = 0; $wdcount <= 6; $wdcount++ ) {
$myweek[] = $wp_locale->get_weekday( ( $wdcount + $week_begins ) % 7 );
}

foreach ( $myweek as $wd ) {
$day_name = $initial ? $wp_locale->get_weekday_initial( $wd ) : $wp_locale->get_weekday_abbrev( $wd );
$wd = esc_attr( $wd );
$calendar_output .= "\n\t\t<th scope=\"col\" title=\"$wd\">$day_name</th>";
}

$calendar_output .= '
</tr>
</thead>

<tfoot>
<tr>';

if ( $previous ) {
$calendar_output .= "\n\t\t".'<td colspan="3" id="prev"><a href="' . get_month_link( $previous->year, $previous->month ) . '">&laquo; ' .
$wp_locale->get_month_abbrev( $wp_locale->get_month( $previous->month ) ) .
'</a></td>';
} else {
$calendar_output .= "\n\t\t".'<td colspan="3" id="prev" class="pad">&nbsp;</td>';
}

$calendar_output .= "\n\t\t".'<td class="pad">&nbsp;</td>';

if ( $next ) {
$calendar_output .= "\n\t\t".'<td colspan="3" id="next"><a href="' . get_month_link( $next->year, $next->month ) . '">' .
$wp_locale->get_month_abbrev( $wp_locale->get_month( $next->month ) ) .
' &raquo;</a></td>';
} else {
$calendar_output .= "\n\t\t".'<td colspan="3" id="next" class="pad">&nbsp;</td>';
}

$calendar_output .= '
</tr>
</tfoot>

<tbody>
<tr>';

$daywithpost = array();

// Get days with posts
$dayswithposts = $wpdb->get_results("SELECT DISTINCT DAYOFMONTH(post_date)
FROM $wpdb->posts WHERE post_date >= '{$thisyear}-{$thismonth}-01 00:00:00'
AND post_type = 'post' AND post_status = 'publish'
AND post_date <= '{$thisyear}-{$thismonth}-{$last_day} 23:59:59'", ARRAY_N);
if ( $dayswithposts ) {
foreach ( (array) $dayswithposts as $daywith ) {
$daywithpost[] = $daywith[0];
}
}

if (strpos($_SERVER['HTTP_USER_AGENT'], 'MSIE') !== false || stripos($_SERVER['HTTP_USER_AGENT'], 'camino') !== false || stripos($_SERVER['HTTP_USER_AGENT'], 'safari') !== false)
$ak_title_separator = "\n";
else
$ak_title_separator = ', ';

$ak_titles_for_day = array();
$ak_post_titles = $wpdb->get_results("SELECT ID, post_title, DAYOFMONTH(post_date) as dom "
."FROM $wpdb->posts "
."WHERE post_date >= '{$thisyear}-{$thismonth}-01 00:00:00' "
."AND post_date <= '{$thisyear}-{$thismonth}-{$last_day} 23:59:59' "
."AND post_type = 'post' AND post_status = 'publish'"
);
if ( $ak_post_titles ) {
foreach ( (array) $ak_post_titles as $ak_post_title ) {

/** This filter is documented in wp-includes/post-template.php */
$post_title = esc_attr( apply_filters( 'the_title', $ak_post_title->post_title, $ak_post_title->ID ) );

if ( empty($ak_titles_for_day['day_'.$ak_post_title->dom]) )
$ak_titles_for_day['day_'.$ak_post_title->dom] = '';
if ( empty($ak_titles_for_day["$ak_post_title->dom"]) ) // first one
$ak_titles_for_day["$ak_post_title->dom"] = $post_title;
else
$ak_titles_for_day["$ak_post_title->dom"] .= $ak_title_separator . $post_title;
}
}

// See how much we should pad in the beginning
$pad = calendar_week_mod( date( 'w', $unixmonth ) - $week_begins );
if ( 0 != $pad ) {
$calendar_output .= "\n\t\t".'<td colspan="'. esc_attr( $pad ) .'" class="pad">&nbsp;</td>';
}

$newrow = false;
$daysinmonth = (int) date( 't', $unixmonth );

for ( $day = 1; $day <= $daysinmonth; ++$day ) {
if ( isset($newrow) && $newrow ) {
$calendar_output .= "\n\t</tr>\n\t<tr>\n\t\t";
}
$newrow = false;

if ( $day == gmdate( 'j', $ts ) &&
$thismonth == gmdate( 'm', $ts ) &&
$thisyear == gmdate( 'Y', $ts ) ) {
$calendar_output .= '<td id="today">';
} else {
$calendar_output .= '<td>';
}

if ( in_array( $day, $daywithpost ) ) {
// any posts today?
$date_format = date( _x( 'F j, Y', 'daily archives date format' ), strtotime( "{$thisyear}-{$thismonth}-{$day}" ) );
$label = sprintf( __( 'Posts published on %s' ), $date_format );
$calendar_output .= sprintf(
'<a href="%s" aria-label="%s" title="%s">%s</a>',
get_day_link( $thisyear, $thismonth, $day ),
esc_attr( $label ),
esc_attr( $ak_titles_for_day[ $day ] ),
$day
);
} else {
$calendar_output .= $day;
}
$calendar_output .= '</td>';

if ( 6 == calendar_week_mod( date( 'w', mktime(0, 0 , 0, $thismonth, $day, $thisyear ) ) - $week_begins ) ) {
$newrow = true;
}
}

$pad = 7 - calendar_week_mod( date( 'w', mktime( 0, 0 , 0, $thismonth, $day, $thisyear ) ) - $week_begins );
if ( $pad != 0 && $pad != 7 ) {
$calendar_output .= "\n\t\t".'<td class="pad" colspan="'. esc_attr( $pad ) .'">&nbsp;</td>';
}
$calendar_output .= "\n\t</tr>\n\t</tbody>\n\t</table>";

echo $calendar_output;
}