pdate/lib/jalali.js

A tiny Persian calender convertor from/to Gregorian calendar

/* jalali.js  Gregorian to Jalali and inverse date convertor
 * Copyright (C) 2001  Roozbeh Pournader <roozbeh@sharif.edu>
 * Copyright (C) 2001  Mohammad Toossi <mohammad@bamdad.org>
 * Copyright (C) 2003  Behdad Esfahbod <js@behdad.org>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You can receive a copy of GNU Lesser General Public License at the
 * World Wide Web address <http://www.gnu.org/licenses/lgpl.html>.
 *
 * For licensing issues, contact The FarsiWeb Project Group,
 * Computing Center, Sharif University of Technology,
 * PO Box 11365-8515, Tehran, Iran, or contact us the
 * email address <FWPG@sharif.edu>.
 */
 
var g_days_in_month = new Array(31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31);
var j_days_in_month = new Array(31, 31, 31, 31, 31, 31, 30, 30, 30, 30, 30, 29);
 
function div(a,b) {
  return Math.floor(a/b);
}

function gregorianToJalali(g /* array containing year, month, day*/ )
{
   var gy, gm, gd;
   var jy, jm, jd;
   var g_day_no, j_day_no;
   var j_np;
 
   var i;

   gy = g[0]-1600;
   gm = g[1]-1;
   gd = g[2]-1;

   g_day_no = 365*gy+div((gy+3),4)-div((gy+99),100)+div((gy+399),400);
   for (i=0;i<gm;++i)
    g_day_no += g_days_in_month[i];
   if (gm>1 && ((gy%4==0 && gy%100!=0) || (gy%400==0)))
    /* leap and after Feb */
    ++g_day_no;
   g_day_no += gd;
 
   j_day_no = g_day_no-79;
 
   j_np = div(j_day_no, 12053);
   j_day_no %= 12053;
 
   jy = 979+33*j_np+4*div(j_day_no,1461);
   j_day_no %= 1461;
 
   if (j_day_no >= 366) {
    jy += div((j_day_no-1),365);
    j_day_no = (j_day_no-1)%365;
   }
 
   for (i = 0; i < 11 && j_day_no >= j_days_in_month[i]; ++i) {
    j_day_no -= j_days_in_month[i];
   }
   jm = i+1;
   jd = j_day_no+1;

   return new Array(jy, jm, jd);
}

function jalaliToGregorian(j /* array containing year, month, day*/ )
{
   var gy, gm, gd;
   var jy, jm, jd;
   var g_day_no, j_day_no;
   var leap;

   var i;

   jy = j[0]-979;
   jm = j[1]-1;
   jd = j[2]-1;

   j_day_no = 365*jy + div(jy,33)*8 + div((jy%33+3),4);
   for (i=0; i < jm; ++i)
    j_day_no += j_days_in_month[i];

   j_day_no += jd;

   g_day_no = j_day_no+79;

   gy = 1600 + 400*div(g_day_no,146097); /* 146097 = 365*400 + 400/4 - 400/100 + 400/400 */
   g_day_no = g_day_no % 146097;

   leap = 1;
   if (g_day_no >= 36525) /* 36525 = 365*100 + 100/4 */
   {
    g_day_no--;
    gy += 100*div(g_day_no,36524); /* 36524 = 365*100 + 100/4 - 100/100 */
    g_day_no = g_day_no % 36524;
    
    if (g_day_no >= 365)
     g_day_no++;
    else
     leap = 0;
   }

   gy += 4*div(g_day_no,1461); /* 1461 = 365*4 + 4/4 */
   g_day_no %= 1461;

   if (g_day_no >= 366) {
    leap = 0;

    g_day_no--;
    gy += div(g_day_no, 365);
    g_day_no = g_day_no % 365;
   }

   for (i = 0; g_day_no >= g_days_in_month[i] + (i == 1 && leap); i++)
    g_day_no -= g_days_in_month[i] + (i == 1 && leap);
   gm = i+1;
   gd = g_day_no+1;

   return new Array(gy, gm, gd);
}

module.exports.jalaliToGregorian = jalaliToGregorian;
module.exports.gregorianToJalali = gregorianToJalali;