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From:	"Buchbinder, Barry (NIH/NIAID) [E]" <BBuchbinder AT niaid DOT nih DOT gov>
To:	"cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>,
	"'cygwin'" <cygwin AT overbearing DOT org>
Date:	Sun, 22 Jan 2012 13:21:13 -0500
Subject:	RE: 1.7.9 : date command fails for year 1900
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cygwin sent the following at Friday, January 20, 2012 7:34 PM

>I'm seeing a problem with my setup where the date command fails in an
>odd way:
>
>this is what it does: $ date -d '1 January 1900' date: invalid date `1
>January 1900'
>
>same thing on a linux box: $ date -d '1 January 1900' Mon Jan 1 00:00:00
>PMT 1900
>
>any dates after 1901 seem to work OK: $ date -d '1 January 1902' Wed Jan
>1 00:00:00 PMT 1902
>
>but nothing works before then:
>
>$ date -d 'today - 150 years' date: invalid date `today - 150 years'
>
>$ date -d 'today - 100 years' Sun Jan 21 01:33:27 WET 1912
>
>this is the info for the date command:
>
>$ date --version date (GNU coreutils) 8.14 Packaged by Cygwin (8.14-1)
>Copyright (C) 2011 Free Software Foundation, Inc. License GPLv3+: GNU
>GPL version 3 or later <http://gnu.org/licenses/gpl.html>. This is
>free software: you are free to change and redistribute it. There is NO
>WARRANTY, to the extent permitted by law.
>
>Written by David MacKenzie.
>
>Where should I start debugging?

Start by finding out exactly when date stops working.

The followijng is the same date version, everything up to date, on
Windws 7:

/c> date -d 1901-12-13\ 15:45:52
Fri, Dec 13, 1901  3:45:52 PM
/c> date -d 1901-12-13\ 15:45:51
date: invalid date `1901-12-13 15:45:51'
/c> date -d 1901-12-13\ 15:45:51.999
date: invalid date `1901-12-13 15:45:51.999'
/c> date -d 1901-12-13\ 15:45:52.000
Fri, Dec 13, 1901  3:45:52 PM

So 1901-12-13 15:45:52 is the earliest that works  Waiting a few minutes
and repeating does not change this.

When is that in seconds:

/c> date -d 1901-12-13\ 15:45:52 +%s
-2147483648

%s give the number of "seconds since 1970-01-01 00:00:00 UTC".  So this
critical time is 2147483648 seconds before the start of the Unix epoch.

Now -2147483648 = -2^31.  So it looks like cygwin date encodes seconds as
signed long integers.  Presumably, date on your linux box was compiled to
use something bigger.

- Barry
  Disclaimer:  Statements made herein are not made on behalf of NIAID.


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