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