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17 years ago
In response to the note whose first line is:
Re note posted by "admin at smitelli dot com"

I believe you have the conversion backwards. You should add an hour to filemtime if the system is in DST and the file is not. Conversely, you should subtract an hour if the file time is DST and the current OS time is not.

Here's a simplified, corrected version:
<?php
    function getmodtime($file) { //returns the time a file was modified.
        $mtime = filemtime($file);
        //date('I') returns 1 if DST is on and 0 if off.
        $diff = date('I')-date('I', $mtime);
        //diff =  0 if file-time and os-time are both in the same DST setting
        //diff =  1 if os is DST and file is not
        //diff = -1 if file is DST and os is not
        return $mtime + $diff*3600;
    }
?>
Here's a test:
<?php
    //create two dummy files:
    $file0 = 'file1.txt';
    $file1 = 'file2.txt';
    file_put_contents($file0, '');
    file_put_contents($file1, '');
    
    $time0=strtotime('Jan 1 2008 10:00'); echo 'Date0 (ST): ' . date(DATE_COOKIE, $time0)."\n";
    $time1=strtotime('Aug 1 2008 10:00'); echo 'Date1 (DT): ' . date(DATE_COOKIE, $time1)."\n";
    touch($file0, $time0); //set file0 to Winter (Non-DST)
    touch($file1, $time1); //set file1 to Summer (DST)
    
    $ftime0 = filemtime($file0);
    $ftime1 = filemtime($file1);
    echo "\nUncorrected: \n";
    echo 'File 0: ' . ($ftime0-$time0) ."\n";
    echo 'File 1: ' . ($ftime1-$time1) ."\n";
    //if your system adjusts for DST, then _one_ of the above should be 3600 or -3600, depending on the time of year
    
    $ftime0 = getmodtime($file0); //use filemtime correction
    $ftime1 = getmodtime($file1); //use filemtime correction
    echo "\nCorrected: \n";
    echo 'File 0: ' . ($ftime0-$time0) ."\n";
    echo 'File 1: ' . ($ftime1-$time1) ."\n";
    //both of the corrected values output should be 0.
?>

Output:
------------------------------
(when run in summer)
------------------------------
Date0 (ST): Tuesday, 01-Jan-08 10:00:00 EST
Date1 (DT): Friday, 01-Aug-08 10:00:00 EDT

Uncorrected: 
File 0: -3600
File 1: 0

Corrected: 
File 0: 0
File 1: 0
------------------------------
(when run in winter--dates omitted)
------------------------------
Uncorrected: 
File 0: 0
File 1: 3600

Corrected: 
File 0: 0
File 1: 0

In response to Re note posted by "admin at smitelli dot com",  your version below gives the following output when substituted into my test:
------------------------------
(when run in summer--dates omitted)
------------------------------
Uncorrected: 
File 0: -3600
File 1: 0

Corrected: 
File 0: -7200
File 1: 0
------------------------------
You can see that the operation is the opposite of what it should be.
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