/**
* Calculates the day of the year for a given date
*
* @param int $year The year, for example: 2000, -1000, 0
* @param int $month The month, from 1 to 12
* @param float $day The day, from 1 to 31, or with decimals
* @return int The day of the year, for example: 1, 2, 365, 366
*/
function aa_date_to_day_of_year($year, $month, $day)
{
if (aa_is_leap_year($year)) {
$K = 1;
} else {
$K = 2;
}
$day_of_year = aa_int(275 * $month / 9) - $K * aa_int(($month + 9) / 12) + $day - 30;
return $day_of_year;
}
/**
* Calculates the Julian day of a date in the Julian calendar
*
* This algorithm is invalid for negative Julian days.
*
* @param int $year The year, for example: 2000, -1000, 0
* @param int $month The month, from 1 to 12
* @param float $day The day, from 1 to 31, or with decimals
* @return int|bool The Julian day, or false on error
*/
function aa_julian_date_to_julian_day($year, $month, $day)
{
if ($month <= 2) {
$year--;
$month += 12;
}
$julian_day = aa_int(365.25 * ($year + 4716)) + aa_int(30.6001 * ($month + 1)) + $day - 1524.5;
if ($julian_day < 0) {
aa_set_error('This algorithm is invalid for negative Julian days.');
return false;
}
return $julian_day;
}
/**
* Calculates the date for a given day in a given year
*
* The calendar in which the year falls is automatically detected.
* This is needed to determine if the year is a leap year.
*
* @param int $year The year, for example: 2000, -1000, 0
* @param int $day_of_year The day of the year, for example: 1, 2, 365, 366
* @return array|bool The date or false on error
* @returns int 0 The year
* @returns int 1 The month
* @returns int 2 The day
*/
function aa_day_of_year_to_date($year, $day_of_year)
{
if (aa_is_leap_year($year)) {
$K = 1;
} else {
$K = 2;
}
if ($day_of_year < 32) {
$month = 1;
} else {
$month = aa_int(($K + $day_of_year) * 9 / 275 + 0.98);
}
$day = $day_of_year - aa_int(275 * $month / 9) + $K * aa_int(($month + 9) / 12) + 30;
return array($year, $month, $day);
}
/**
* Calculates the date from a Julian day
*
* The calendar in which the date falls is automatically detected.
* This algorithm is invalid for negative Julian days.
*
* @param int $julian_day The Julian day
* @return array|bool The date or false on error
* @returns int 0 The year
* @returns int 1 The month
* @returns float 2 The day
*/
function aa_julian_day_to_date($julian_day)
{
if ($julian_day < 0) {
aa_set_error('This algorithm is invalid for negative Julian days.');
return false;
}
$julian_day += 0.5;
$Z = aa_int($julian_day);
$F = $julian_day - $Z;
// fixes Meeus original algorithm (p. 63) to calculate the Julian day of the change of calendar
// the value of 2299161 is the Julian day for 1582-10-15 in the Gregorian calendar + 0.5
// 1582-10-15 is the default first day of the Gregorian calendar
list($change_year, $change_month, $change_day) = aa_get_calendar_change_date();
$change_julian_day = aa_gregorian_date_to_julian_day($change_year, $change_month, $change_day);
$change_julian_day += 0.5;
if ($Z < $change_julian_day) {
$A = $Z;
} else {
$alpha = aa_int(($Z - 1867216.25) / 36524.25);
$A = $Z + 1 + $alpha - aa_int($alpha / 4);
}
$B = $A + 1524;
$C = aa_int(($B - 122.1) / 365.25);
$D = aa_int(365.25 * $C);
$E = aa_int(($B - $D) / 30.6001);
$day = $B - $D - aa_int(30.6001 * $E) + $F;
if ($E < 14) {
$month = $E - 1;
} else {
if ($E == 14 or $E == 15) {
$month = $E - 13;
} else {
aa_set_error('The calculated value of the month is out of range.');
return false;
}
}
if ($month > 2) {
$year = $C - 4716;
} else {
$year = $C - 4715;
}
return array($year, $month, $day);
}
