From: B.Gilli/G.Filippi
                                                        Date: 11 Nov 1999

             VLT-SW-OCT99 - Y2000 PORTABILITY GUIDELINES
             ===========================================


The following is a brief check list on how to make an application Year2000
compliant. A more complete discussion about Y2K compliance can be found in
the VLT-TRE-ESO-17210-1704, issue 1.1, "Technical Report on YEAR 2000
compliance, Guidelines for VLT Control Software", (available
from patchedFiles/y2k_tre1.1.ps).


1) Identify places for potential problems:
=========================================
Wherever time and date is accessed or manipulated, there is a potential 
problem.  

A list of known potentially dangerous patterns (file "compat.Y2000.config")
to be used by the standard compat utility that searches in SOURCE files
See compat(7) man-page for how to use the utility on your application code.
Applicable to both SUN & HP.


2) Check for necessary changes:
==============================
For every identified potential problem, inspect the code and decide on a case 
basis if changes are required. The basic rule is to avoid any ambiguity that 
could produce future mis-interpretation, and remove usage of obsolete features.
If possible, usage of obsolescent features should also be avoided.
The following is a list of known cases:

* STRUCTURES
------------
 - The usage of struct tm, field tm_year is potentially dangerous. Use 
   ccsTIMEVAL structures for LCC/CCS based applications or at least 32-bit 
   signed or better unsigned time_t types. This will insure proper behavior
   until year 2038. (64 bits will be necessary later on!)
 - Two digit year representation: yy-mm-dd is forbidden. Always use ISO 
   8601 standard: ccyy-mm-dd with the 4 digits format to express the year 
   in all ASCII representation of a date.


* FUNCTIONS
-----------
 - strptime() and getdate() shall be avoided, in particular without the 
   format specifier %Y(capital). Rather use CCS/tims functions with the 
   following restrictions:
   . timsTimeToString(3) is not compliant, is now obsolete and 
     replaced by timsTimeToIsoString(3)
   . timsStringToTime(3) is not compliant, is now obsolete, 
     and replaced by timsIsoStringToTime(3)

* SCRIPTS & SYSTEM COMMANDS
---------------------------
 - date command: avoid the %y (lowercase) specifier. Rather use the 
   %Y(uppercase) one.
 - troff scripts avoid formatting with \n(yr as yr will be a 2 digit 
   year.
 - clock format command for Tcl: avoid %y(lowercase) specifier. Use 
   only %Y(uppercase).

pay attention to the usage of the following commands:

 - date should have been upgraded to accept optional century digits (%Y 
   specifier accepted).
 - prs,get will never accept century digits. They will rather use the 
   rule that years in the range [69-99] refer to twentieth century while values 
   within [00-68]refer to twenty-first one.
 - touch is presently not always able to handle -t option with dates 
   later than midnight January 1 2000 should be upgraded with OS patches.


3) Remove obsolescent VLTSW functions.
====================================== 
Some VLTSW functions have been declared obsolescent in FEB99, and are
removed in the OCT99 version. 

Existing applications should replace such functions with the proper
new ones.


4) test the modified applications & redeploy it.
===============================================
The proper behavior of the application should be tested, including 
identification of possible backwards incompatibilities. 

The critical dates to be tested are:

rollover from 31/12/1999 to 1/1/2000
rollover from 28/2/2000 to 29/2/2000 and next one to 1/3/2000 (Year 2000 is a 
leap year)

A complete report on the Y2K tests done at ESO for the 
VLT Common Sw is posted on the web:
http://www.eso.org/projects/vlt/sw-dev/control-model/index.html

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