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Bug #72096 Swatch time value incorrect for dates before 1970
Submitted: 2016-04-24 18:54 UTC Modified: 2016-04-24 21:06 UTC
From: p987b at davewilliamsmedia dot com Assigned:
Status: Closed Package: Date/time related
PHP Version: 5.6.20 OS: Windows
Private report: No CVE-ID:
 [2016-04-24 18:54 UTC] p987b at davewilliamsmedia dot com
Description:
------------
For dates prior to 1970, (i.e. dates represented by a negative unix timestamp value), swatch values produced by the gmdate() function using format character 'B' are incorrectly rounded-up. They consequently differ from the values produced for identical times of day on dates after 1970, as these are correctly rounded-down.
This problem occurs on PHP 5.3 as well as 5.6.  

Test script:
---------------
for ($unix=1461283200;$unix<=1461369600;$unix+=8000)
	{
	echo "\n  Time:".gmdate('Y-m-d H:i:s = B  ',$unix);
	echo "  Time:".gmdate('Y-m-d H:i:s = B  ',$unix-2592000000);
	}

Expected result:
----------------
I would expect the three-digit swatch time values produced for the 1934 date (right-hand column) to be identical to the swatch values produced for the 2016 date (left-hand column), for any given time of day.

Actual result:
--------------
  Time:2016-04-22 00:00:00 = 041    Time:1934-03-04 00:00:00 = 041  
  Time:2016-04-22 02:13:20 = 134    Time:1934-03-04 02:13:20 = 135  
  Time:2016-04-22 04:26:40 = 226    Time:1934-03-04 04:26:40 = 227  
  Time:2016-04-22 06:40:00 = 319    Time:1934-03-04 06:40:00 = 320  
  Time:2016-04-22 08:53:20 = 412    Time:1934-03-04 08:53:20 = 413  
  Time:2016-04-22 11:06:40 = 504    Time:1934-03-04 11:06:40 = 505  
  Time:2016-04-22 13:20:00 = 597    Time:1934-03-04 13:20:00 = 598  
  Time:2016-04-22 15:33:20 = 689    Time:1934-03-04 15:33:20 = 690  
  Time:2016-04-22 17:46:40 = 782    Time:1934-03-04 17:46:40 = 783  
  Time:2016-04-22 20:00:00 = 875    Time:1934-03-04 20:00:00 = 875  
  Time:2016-04-22 22:13:20 = 967    Time:1934-03-04 22:13:20 = 968   

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 [2016-04-24 21:06 UTC] requinix@php.net
-Status: Open +Status: Verified
 [2016-04-24 21:06 UTC] requinix@php.net
Done some digging around. Yadda yadda yadda, the time is supposed to be calculated as floor(seconds past midnight in UTC+1 / 86.4). The ext/date code uses integer division, and with the negative numbers it explains the accidental rounding up.

The official website <http://www.swatch.com/en_us/internet-time/> has the same bug, but it looks like they're running PHP so...
 [2017-03-09 15:46 UTC] nikic@php.net
Automatic comment on behalf of php@mcq8.be
Revision: http://git.php.net/?p=php-src.git;a=commit;h=b224e7426713befd7449117afd68355231f9077e
Log: Fixed bug #72096 Swatch time value incorrect for dates before 1970
 [2017-03-09 15:46 UTC] nikic@php.net
-Status: Verified +Status: Closed
 
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