Comparing software versions ...

compare_version.php

<?php

function compare_version($version_a, $version_b, $limit = 2)
{
    $a_segments = explode('.', $version_a);
    $b_segments = explode('.', $version_b);
    
    $sentinel = min(sizeof($a_segments), $limit);
    
    for ($i = 0; $i < $sentinel; $i++)
    {
        $a = (isset($a_segments[$i])) ? $a_segments[$i] : 0;
        $b = (isset($b_segments[$i])) ? $b_segments[$i] : 0;

        if ($a != $b)
        {
            if ($a > $b) return 1;
            else if ($a < $b) return -1;
        }
    }

    return 0;
}

test_compare_version.php

<?php

$comparisons = array(
    array('2.10.11', '2.11.5', -1),
    array('2.13.15', '2.2.3', 1),
    array('1.1.1', '1.1.1', 0)
);

foreach ($comparisons as $k => $comparison)
{
    list($a, $b, $expected) = $comparison;
    $actual = ci_version_compare($a, $b);
    $test = "{$actual} == {$expected}; // {$a} and {$b} ({$expected})";
    assert($test);
}