139 lines
4.1 KiB
Perl
139 lines
4.1 KiB
Perl
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package Time::Local;
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require 5.000;
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require Exporter;
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use Carp;
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@ISA = qw(Exporter);
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@EXPORT = qw(timegm timelocal);
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=head1 NAME
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Time::Local - efficiently compute time from local and GMT time
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=head1 SYNOPSIS
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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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=head1 DESCRIPTION
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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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Both routines return -1 if the integer limit is hit. I.e. for dates
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after the 1st of January, 2038 on most machines.
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=cut
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BEGIN {
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$SEC = 1;
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$MIN = 60 * $SEC;
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$HR = 60 * $MIN;
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$DAY = 24 * $HR;
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$epoch = (localtime(2*$DAY))[5]; # Allow for bugs near localtime == 0.
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$YearFix = ((gmtime(946684800))[5] == 100) ? 100 : 0;
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}
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sub timegm {
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$ym = pack(C2, @_[5,4]);
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$cheat = $cheat{$ym} || &cheat;
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return -1 if $cheat<0 and $^O ne 'VMS';
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$cheat + $_[0] * $SEC + $_[1] * $MIN + $_[2] * $HR + ($_[3]-1) * $DAY;
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}
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sub timelocal {
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my $t = &timegm;
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my $tt = $t;
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my (@lt) = localtime($t);
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my (@gt) = gmtime($t);
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if ($t < $DAY and ($lt[5] >= 70 or $gt[5] >= 70 )) {
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# Wrap error, too early a date
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# Try a safer date
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$tt = $DAY;
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@lt = localtime($tt);
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@gt = gmtime($tt);
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}
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my $tzsec = ($gt[1] - $lt[1]) * $MIN + ($gt[2] - $lt[2]) * $HR;
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my($lday,$gday) = ($lt[7],$gt[7]);
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if($lt[5] > $gt[5]) {
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$tzsec -= $DAY;
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}
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elsif($gt[5] > $lt[5]) {
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$tzsec += $DAY;
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}
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else {
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$tzsec += ($gt[7] - $lt[7]) * $DAY;
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}
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$tzsec += $HR if($lt[8]);
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$time = $t + $tzsec;
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return -1 if $cheat<0 and $^O ne 'VMS';
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@test = localtime($time + ($tt - $t));
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$time -= $HR if $test[2] != $_[2];
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$time;
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}
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sub cheat {
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$year = $_[5];
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$year -= 1900
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if $year > 1900;
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$month = $_[4];
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croak "Month '$month' out of range 0..11" if $month > 11 || $month < 0;
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croak "Day '$_[3]' out of range 1..31" if $_[3] > 31 || $_[3] < 1;
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croak "Hour '$_[2]' out of range 0..23" if $_[2] > 23 || $_[2] < 0;
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croak "Minute '$_[1]' out of range 0..59" if $_[1] > 59 || $_[1] < 0;
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croak "Second '$_[0]' out of range 0..59" if $_[0] > 59 || $_[0] < 0;
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$guess = $^T;
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@g = gmtime($guess);
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$year += $YearFix if $year < $epoch;
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$lastguess = "";
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$counter = 0;
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while ($diff = $year - $g[5]) {
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croak "Can't handle date (".join(", ",@_).")" if ++$counter > 255;
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$guess += $diff * (363 * $DAY);
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@g = gmtime($guess);
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if (($thisguess = "@g") eq $lastguess){
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return -1; #date beyond this machine's integer limit
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}
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$lastguess = $thisguess;
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}
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while ($diff = $month - $g[4]) {
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croak "Can't handle date (".join(", ",@_).")" if ++$counter > 255;
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$guess += $diff * (27 * $DAY);
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@g = gmtime($guess);
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if (($thisguess = "@g") eq $lastguess){
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return -1; #date beyond this machine's integer limit
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}
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$lastguess = $thisguess;
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}
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@gfake = gmtime($guess-1); #still being sceptic
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if ("@gfake" eq $lastguess){
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return -1; #date beyond this machine's integer limit
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}
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$g[3]--;
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$guess -= $g[0] * $SEC + $g[1] * $MIN + $g[2] * $HR + $g[3] * $DAY;
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$cheat{$ym} = $guess;
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}
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1;
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