#!/bin/ksh

# Calendar date from Julian Day Number
julian2date()
{
typeset tmpday=$(($1 - 1721119))
typeset centuries=$(( (4 * tmpday - 1) / 146097))
tmpday=$((tmpday + centuries - centuries/4))
typeset year=$(( (4 * tmpday - 1) / 1461))
tmpday=$((tmpday - (1461 * year) / 4))
typeset month=$(( (10 * tmpday - 5) / 306))
day=$((tmpday - (306 * month + 5) / 10))
month=$((month + 2))
year=$((year + month/12))
month=$((month % 12 + 1))
printf "%s %02d %02d" $year $month $day
}

date2julian() #  year month day
{
  typeset year=$1;  typeset month=$2;  typeset day=$3
  typeset tmpmonth=$((12 * year + month - 3))
  typeset tmpyear=$((tmpmonth / 12))
  print $(( (734 * tmpmonth + 15) / 24 -  2 * tmpyear + \
  tmpyear/4 - tmpyear/100 + tmpyear/400 + day + 1721119 ))
}


printf "today->[2005 4 29] julian->[%d]\n" $(date2julian 2005 4 29)
printf "and back from julian->[%s %s %s]\n" $(julian2date $(date2julian 2005 4 29))