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;# timelocal.pl
;#
;# Usage:
;# $time = timelocal($sec,$min,$hours,$mday,$mon,$year);
;# $time = timegm($sec,$min,$hours,$mday,$mon,$year);
;# These routines are quite efficient and yet are always guaranteed to agree
;# with localtime() and gmtime(). We manage this by caching the start times
;# of any months we've seen before. If we know the start time of the month,
;# we can always calculate any time within the month. The start times
;# themselves are guessed by successive approximation starting at the
;# current time, since most dates seen in practice are close to the
;# current date. Unlike algorithms that do a binary search (calling gmtime
;# once for each bit of the time value, resulting in 32 calls), this algorithm
;# calls it at most 6 times, and usually only once or twice. If you hit
;# the month cache, of course, it doesn't call it at all.
;# timelocal is implemented using the same cache. We just assume that we're
;# translating a GMT time, and then fudge it when we're done for the timezone
;# and daylight savings arguments. The timezone is determined by examining
;# the result of localtime(0) when the package is initialized. The daylight
;# savings offset is currently assumed to be one hour.
CONFIG: {
package timelocal;
local($[) = 0;
@epoch = localtime(0);
$tzmin = $epoch[2] * 60 + $epoch[1]; # minutes east of GMT
if ($tzmin > 0) {
$tzmin = 24 * 60 - $tzmin; # minutes west of GMT
$tzmin -= 24 * 60 if $epoch[5] == 70; # account for the date line
}
$SEC = 1;
$MIN = 60 * $SEC;
$HR = 60 * $MIN;
$DAYS = 24 * $HR;
$YearFix = ((gmtime(946684800))[5] == 100) ? 100 : 0;
}
sub timegm {
package timelocal;
local($[) = 0;
$ym = pack(C2, @_[5,4]);
$cheat = $cheat{$ym} || &cheat;
$cheat + $_[0] * $SEC + $_[1] * $MIN + $_[2] * $HR + ($_[3]-1) * $DAYS;
}
sub timelocal {
package timelocal;
local($[) = 0;
$time = &main'timegm + $tzmin*$MIN;
@test = localtime($time);
$time -= $HR if $test[2] != $_[2];
$time;
}
package timelocal;
sub cheat {
$year = $_[5];
$month = $_[4];
die "Month out of range 0..11 in ctime.pl\n" if $month > 11;
$guess = $^T;
@g = gmtime($guess);
$year += $YearFix if $year < $epoch[5];
while ($diff = $year - $g[5]) {
$guess += $diff * (363 * $DAYS);
@g = gmtime($guess);
}
while ($diff = $month - $g[4]) {
$guess += $diff * (27 * $DAYS);
@g = gmtime($guess);
}
$g[3]--;
$guess -= $g[0] * $SEC + $g[1] * $MIN + $g[2] * $HR + $g[3] * $DAYS;
$cheat{$ym} = $guess;
}
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