human-readable date differences

Michael Barton — Wed, 21 Dec 2005 11:29:32 +0000

I had an idea today. I wanted to include human-readable ages beside some of the dates on my blog (e.g. “1 day, 8 hours ago”). I searched around a bit, and all of the solutions I found just divide the difference in seconds by 31536000 to get years and so on. It doesn’t take leap years or different-sized months into account.

Today is December 21, 2005. To me, 2 years, 2 months ago was October 21, 2003.

It took a while to write. The first version used brute force to get the difference out of mktime. That worked perfectly but was slow. I used it to generate a bunch of test cases, though.

What I eventually figured out is that you can just subtract the beginning years, months, hours, etc. from the current ones. After that, use borrowing similar to long subtraction to get rid of any negative numbers. Seconds borrow 60 from a minute, hours borrow 24 from a day, days borrow from an array of month lengths. You get the idea. Anyway, here’s the code, which I’ll post on the SmartyPlugins wiki as soon as I figure out how.

<?php

/**
 * Smarty plugin
 * -----------------------------------------
 * File:    modifier.human_age.php
 * Type:    modifier
 * Name:    human_age
 * Params:  from_time    unix timestamp (required)
 *          to_time      unix timestamp (default=false (means now))
 *          strip_zeroes remove units with zero values ("0 days") (default=true)
 *          limit        limit the number of units returned (default=no limit)
 * Author:  Michael Barton (http://www.weirdlooking.com/email)
 * Purpose: Returns a human-readable difference between two times
 *          e.g. "1 day, 8 hours, 48 minutes, 57 seconds"
 * Remarks: Correct for leap years and different-sized months.
 *          Well, my idea of correct.  Turns out it's slightly subjective.
 *
 * @link http://www.weirdlooking.com/blog/45
 * -----------------------------------------
 */
  require_once $smarty->_get_plugin_filepath('shared','make_timestamp');

  function smarty_modifier_human_age($from_time, $to_time = false, $strip_zeroes = true, $limit = false)
  {
    if ($to_time === false)
      $to_time = time();
    $order = array('year', 'mon', 'mday', 'hours', 'minutes', 'seconds');
    $names = array('year', 'month', 'week', 'day', 'hour', 'minute', 'second');
    $sizes = array(12, 2=>24, 60, 60);
    $month_lengths = array(31, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30);
    $from = getdate($from_time);
    $to = getdate($to_time);
    $delta = array();
    foreach ($order as $unit)
      $delta[] = $to[$unit] - $from[$unit];
    for ($i = 5; $i >= 0; $i--)
      if ($delta[$i] < 0)
      {
        $delta[$i-1]--;
        if ($i == 2 && ($to['mon'] == 3 && !($to['year'] % 4)))
          $delta[$i] += 29; // fix this before the year 2100!!!
        else if ($i == 2)
          $delta[$i] +=  $month_lengths[$to['mon']-1];
        else
          $delta[$i] += $sizes[$i-1];
      }
    $delta[2] -= ($week = floor($delta[2]/7)) * 7;
    $delta = array($delta[0], $delta[1], $week, $delta[2], $delta[3], $delta[4], $delta[5]);
    $ret = array();
    foreach ($delta as $i => $val)
      if (($delta[$i] || !$strip_zeroes) && ($limit === false || sizeof($ret) < $limit))
        $ret[] = $delta[$i].' '.$names[$i].($delta[$i] == 1 ? '' : 's');
    return join(', ', $ret);
  }
?>

WeirdLooking.com: Michael Barton's Blog

human-readable date differences