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### Re: Portable previous dates

by vt220 (Scribe)
 on Jul 09, 2011 at 00:31 UTC ( #913450=note: print w/replies, xml ) Need Help??

in reply to Portable previous dates

A long while back, after finding these:

http://alcor.concordia.ca/~gpkatch/gdate-algorithm.html
http://www.smart.net/~mmontes/ushols.html

I put together the following subs. Please note that I add or subtract 3 in the conversion routines. This allows a modulo function to return the day of the week with 0 equaling Sunday. As in:

```\$DoW = \$gdate % 7;

I humbly submit the following for review...

```#===================================================================
#   d2g() Convert year, month, and day to date factor G.

sub d2g {
my(\$y, \$m, \$d) = @_;
my \$g;
\$m = (\$m + 9) % 12;
\$y = \$y - int(\$m/10);
\$g = 365*\$y + int(\$y/4) - int(\$y/100) + int(\$y/400) + int((\$m*306
++ 5)/10) + (\$d - 1);
#-------
\$g += 3;
return \$g;
}

#====================================================================
#   g2d() Convert date factor G to year, month, and day.

sub g2d {
my(\$g) = @_;
my(\$y, \$m, \$d, \$M, \$D);
#-----------------------------------
\$g -= 3;
#-------
\$y = int((10000*\$g + 14780)/3652425);
\$D = \$g - (365*\$y + int(\$y/4) - int(\$y/100) + int(\$y/400));

if  ( \$D < 0 ) {
\$y = \$y - 1;
\$D = \$g - (365*\$y + int(\$y/4) - int(\$y/100) + int(\$y/400));
}

\$M = int((100*\$D + 52)/3060);
\$m = (\$M + 2)%12 + 1;
\$y = \$y + int((\$M + 2)/12);
\$d = \$D - int((\$M*306 + 5)/10) + 1;
return (\$y, \$m, \$d);
}

#====================================================================
#   ValidYMD() Returns true if given year, month, and day is valid.

sub ValidYMD {
my(\$y, \$m, \$d) = @_;
my(\$Y, \$M, \$D) = g2d( d2g(\$y, \$m, \$d) );
return \$y == \$Y && \$m == \$M && \$d == \$D;
}

Replies are listed 'Best First'.
Re^2: Portable previous dates
by Anonymous Monk on Jul 09, 2011 at 13:29 UTC
Thanks for the response vt220, will review this code and see what I can learn from it. Darryl

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