Bug #9076 Updated: GregorianToJD function returns incorrect values

ID: 9076 Updated by: jmoore Reported By: basil.hussain@specialreserve.net Old-Status: Open Status: Assigned Bug Type: Calendar related PHP Version: 4.0.4pl1 Assigned To: jmoore Comments: Ill look at these patches at some point soon. - James Previous Comments: --------------------------------------------------------------------------- [2001-02-09 07:15:34] basil.hussain@specialreserve.net I found more thoroughly-researched algorithms for calculating to and from Gregorian/Julian calender dates to Julian Day Count values: http://www.capecod.net/~pbaum/date/date0.htm I suggest that the PHP Calender functions be based upon the algorithms here, as meticulous care seems to have been taken to formulate and proof them. In the meantime, I have written my own implementations of the GregorianToJD and JDToGregorian functions in PHP. I have tested them using the examples in Table 2 of Chapter 1 of Baum's work and they pass. function php_gregoriantojd($input_year, $input_month, $input_day) { // Make sure supplied arguments are of the correct form. Day may be a fractional value, // but month and year must be integers. $input_year = intval($input_year); $input_month = intval($input_month); $input_day = doubleval($input_day); // Adjust the start of the year so that it is in March. if($input_month < 3) { $input_month += 12; $input_year -= 1; } // Calculate and return the Julian Day Count. return $input_day + floor((153 * $input_month - 457) / 5) + 365 * $input_year + floor($input_year / 4) - floor($input_year / 100) + floor($input_year / 400) + 1721118.5; } function php_jdtogregorian($jdc) { // Make sure that the Julian Day Count value is proper. $jdc = doubleval($jdc); $z = floor($jdc - 1721118.5); $r = $jdc - 1721118.5 - $z; $g = $z - 0.25; $a = floor($g / 36524.25); $b = $a - floor($a / 4); $gregorian["year"] = floor(($b + $g) / 365.25); $c = $b + $z - floor(365.25 * $gregorian["year"]); $gregorian["month"] = floor((5 * $c + 456) / 153); $gregorian["day"] = $c - floor((153 * $gregorian["month"] - 457) / 5) + $r; if($gregorian["month"] > 12) { $gregorian["year"] += 1; $gregorian["month"] -= 12; } return $gregorian; } The line breaks on all of that will probably be all mangled when I post, but it should make sense when straightened out... --------------------------------------------------------------------------- [2001-02-02 11:05:26] basil.hussain@specialreserve.net The GregorianToJD Calender function returns incorrect results. As far as I can tell, this applies to the GregorianToSdn internal function in the PHP source. There's not really any point putting a sample PHP script here, as it's the algorithm that seems to be at fault. I took two specific cases and worked through the algorithm by hand (i.e. pen and paper). Here are the results: 2nd February 2001 (2/2/2001) = 2451943 7th June 1980 (7/6/1980) = 2473618 As I understand it, the Julian Day Count is a uniform count of days from some time around 4714 BC. Now, how can 2/2/01 be a lesser number of days than 7/6/80? I have no idea what the correct results for these test cases are, nor any idea what particular part of the algorithm is wrong. It's just wrong somewhere! --------------------------------------------------------------------------- ATTENTION! Do NOT reply to this email! To reply, use the web interface found at http://bugs.php.net/?id=9076&edit=2