Hijri calendar support in glibc

[أحمد المحمودي <aelmahmoudy at users dot sourceforge dot net>]

as-salamu alaykom,

  I have been doing some research about the possibility of adding hijri 
  calendar directly into glibc.
  I found that glibc does support other calendars, such as Buddhist Era 
  (using in Thailand, and Laos I think) and the Japanese Emperors' 
  reigns.

  That is done by adding definitions for era, era_d_t_fmt, era_d_fmt, 
  era_t_fmt, and alt_digits in the locale [1].

  Those definitions modify the behaviour of some time functions (such as 
  strftime) when E and O modifiers are used [2].

  The format of 'era' consists of semicolon-separated strings. Each 
  string shall be an era description segment with the format:

  direction:offset:start_date:end_date:era_name:era_format

  The descriptions for each field are in [1].

  Now the problem is that supported calendars are those which are based  
  on Gregorian calendar. In [3] it says:

  The E modifier supports alternative date formats, such as the Japanese 
  Emperor's Era, as long as these are based on the Gregorian calendar 
  system. Extending the E modifiers to other date elements may provide 
  an implementation-defined extension capable of supporting other 
  calendar systems, especially in combination with the O modifier.

  So, I was thinking, that this 'era' can be used for Hijri as follows:

  1. For countries that formally use Hijri system, we can add an 'era' 
  definition in their respective locale files. The era field that 
  matters now is 'era_name'. It can be something like "A.H." or even 
  "ه".

  2. In glibc C code: a conversion function from Gregorian to Hijri can 
  be added, I was thinking of using the conversion functions that 
  implement the Um-Ul-Qura algorithm since, as far as I know, this is 
  the algorithm that is formally used in Arabia.

  3. Somewhere in glibc's time/strftime_l.c & time/strptime_l.c [4], the 
  code should check if era_name is "A.H" or "ه", if that is true, it 
  will call for the conversion function to get the appropriate Hijri 
  date.

  I hope to get your comments on this suggestion.

  [1] http://www.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap07.html#tag_07_03_05
  [2] http://www.gnu.org/software/libc/manual/html_node/Formatting-Calendar-Time.html#Formatting-Calendar-Time
  [3] http://www.opengroup.org/onlinepubs/009695399/utilities/date.html
  [4] http://sources.redhat.com/cgi-bin/cvsweb.cgi/libc/time/strftime_l.c?cvsroot=glibc
    & http://sources.redhat.com/cgi-bin/cvsweb.cgi/libc/time/strptime_l.c?cvsroot=glibc

-- 
 أحمد المحمودي (Ahmed El-Mahmoudy)
  Digital design engineer
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