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Re^2: What about Easter?

by pg (Canon)
on Jul 24, 2005 at 17:24 UTC ( #477590=note: print w/replies, xml ) Need Help??


in reply to Re: What about Easter?
in thread What about Easter?

Okay I ported whatever is in the last post of that thread to Perl: (only tested with this year though)

print easter_date(2005); sub easter_date { my $Year = shift; $G = $Year % 19; $C = int($Year / 100); $H = int($C - ($C / 4) - ((8*$C+13) / 25) + 19*$G + 15) % 30; + $I = $H - int($H / 28)*(1 - int($H / 28)*int(29 / ($H + 1))*( +int(21 - $G) / 11)); $J = ($Year + int($Year/4) + $I + 2 - $C + int($C/4)) % 7; $L = $I - $J; $m = 3 + int(($L + 40) / 44); $d = $L + 28 - 31 * (int($m / 4)); $y = $Year; return sprintf("%04d-%02d-%02d", $y, $m, $d); }

Replies are listed 'Best First'.
Re^3: What about Easter?
by greenFox (Vicar) on Jul 25, 2005 at 02:24 UTC

    DON'T USE THIS CODE!

    I wrote a quick and dirty compare of the date calculated by this sub against the list in the zip file at Easter Sunday Dates and found it to be 22% inaccurate. Good enough for PHP perhaps? *grin*

    Yes I get that the thread was a joke :)

    Update: see Re^3: What about Easter? by themage for an updated subroutine which does not produce any erros when compared to the list.

    --
    Murray Barton
    Do not seek to follow in the footsteps of the wise. Seek what they sought. -Basho

Re^3: What about Easter?
by themage (Friar) on Jul 25, 2005 at 12:19 UTC
    There is a small error in the PHP version, that pg ported here: <updated, wrong name>.

    The line
    $H = int($C - ($C / 4) - ((8*$C+13) / 25) + 19*$G + 15) % 30;

    Should be:
    $H = ($C - int($C / 4) - int((8*$C+13) / 25) + 19*$G + 15) % 30;

    The final sub sould look like:

    sub easter_date { my $Year = shift; my ($G,$C,$H,$I,$J,$L)="0"x6; $G = $Year % 19; $C = int($Year / 100); $H = ($C - int($C / 4) - int((8*$C+13) / 25) + 19*$G + 15) % 30; $I = $H - int($H / 28)*(1 - int($H / 28)*int(29 / ($H + 1))*(int(21 +- $G) / 11)); $J = ($Year + int($Year/4) + $I + 2 - $C + int($C/4)) % 7; $L = $I - $J; my $m = 3 + int(($L + 40) / 44); my $d = $L + 28 - 31 * (int($m / 4)); my $y = $Year; return sprintf("%04d-%02d-%02d", $y, $m, $d); }
    This way, I think that it should be ok. What you think greenFox?

      That fixed it. With your updated sub I got 0 errors for 2517 dates. Well spotted.

      --
      Murray Barton
      Do not seek to follow in the footsteps of the wise. Seek what they sought. -Basho

Re^3: What about Easter?
by m.att (Pilgrim) on Jul 24, 2005 at 17:35 UTC
    Too SLOW! Must be in CORE!

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