Boolean bitpacking for PHP

bitpack.php

<?php

/**
 * Given an array of numbers (of 24 bits/hours),
 * where each bit of the number is equal to 1 hour,
 * validates if the corresponding hour and day is on.
 *
 * @param $days Array of ~24 bits numbers.
 * @param $day Number from 0 to 7
 * @param $hour 0 to 23
 *
 * @return bool
 */
function isHourOn($days, $day, $hour) {
    return isset($days[$day]) 
       and $days[$day] > 0
       and (($days[$day] >> $hour) & 1);
}

/**
 * Given an array of numbers, convert them to
 * a number, where each number is validated to
 * be different to 0 and them added to the bits
 * of the result number.
 *
 * @param $hours Array of numbers.
 *
 * @return numeric
 */
function packHours($hours) {
    $a = 0;
    $i = 0;
    foreach ($hours as $h) {
        $a |= (($h > 0) << $i);
        if (++$i >= 24)
            break;
    }
    return $a;
}

/**
 * Convert a ~24 bits number into an array
 * of integers (0's and 1's)
 *
 * @param $pack Number of ~24bits
 *
 * @return Array
 */
function unpackHours($pack) {
    $hrs = array_fill(0, 23, 0);
    for ($i = 0; $i < 24; $i++) {
        $hrs[$i] = ($pack >> $i) & 1;
    }
    return $hrs;
}