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246 lines
7.8 KiB
246 lines
7.8 KiB
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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@EXPORT_OK = qw( timegm_nocheck timelocal_nocheck );
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# Set up constants
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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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# Determine breakpoint for rolling century
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my $thisYear = (localtime())[5];
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$nextCentury = int($thisYear / 100) * 100;
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$breakpoint = ($thisYear + 50) % 100;
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$nextCentury += 100 if $breakpoint < 50;
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my %options;
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sub timegm {
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my (@date) = @_;
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if ($date[5] > 999) {
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$date[5] -= 1900;
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}
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elsif ($date[5] >= 0 && $date[5] < 100) {
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$date[5] -= 100 if $date[5] > $breakpoint;
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$date[5] += $nextCentury;
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}
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$ym = pack(C2, @date[5,4]);
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$cheat = $cheat{$ym} || &cheat(@date);
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$cheat
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+ $date[0] * $SEC
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+ $date[1] * $MIN
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+ $date[2] * $HR
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+ ($date[3]-1) * $DAY;
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}
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sub timegm_nocheck {
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local $options{no_range_check} = 1;
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&timegm;
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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]) * $HR;
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if($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 + $tzsec;
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@test = localtime($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 timelocal_nocheck {
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local $options{no_range_check} = 1;
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&timelocal;
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}
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sub cheat {
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$year = $_[5];
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$month = $_[4];
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unless ($options{no_range_check}) {
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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 || $_[0] < 0;
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}
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$guess = $^T;
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@g = gmtime($guess);
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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 $lastguess){
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croak "Can't handle date (".join(", ",@_).")";
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#date beyond this machine's integer limit
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}
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$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 $lastguess){
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croak "Can't handle date (".join(", ",@_).")";
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#date beyond this machine's integer limit
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}
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$lastguess = $thisguess;
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}
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@gfake = gmtime($guess-1); #still being sceptic
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if ("@gfake" eq $lastguess){
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croak "Can't handle date (".join(", ",@_).")";
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#date beyond this machine's integer limit
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}
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$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} = $guess;
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}
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1;
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__END__
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=head1 NAME
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Time::Local - efficiently compute time from local and GMT time
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=head1 SYNOPSIS
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$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 the inverse of built-in perl fuctions localtime()
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and gmtime(). They accept a date as a six-element array, and return
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the corresponding time(2) value in seconds since the Epoch (Midnight,
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January 1, 1970). This value can be positive or negative.
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It is worth drawing particular attention to the expected ranges for
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the values provided. While the day of the month is expected to be in
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the range 1..31, the month should be in the range 0..11.
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This is consistent with the values returned from localtime() and gmtime().
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The timelocal() and timegm() functions perform range checking on the
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input $sec, $min, $hours, $mday, and $mon values by default. If you'd
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rather they didn't, you can explicitly import the timelocal_nocheck()
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and timegm_nocheck() functions.
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use Time::Local 'timelocal_nocheck';
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{
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# The 365th day of 1999
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print scalar localtime timelocal_nocheck 0,0,0,365,0,99;
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# The twenty thousandth day since 1970
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print scalar localtime timelocal_nocheck 0,0,0,20000,0,70;
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# And even the 10,000,000th second since 1999!
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print scalar localtime timelocal_nocheck 10000000,0,0,1,0,99;
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}
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Your mileage may vary when trying these with minutes and hours,
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and it doesn't work at all for months.
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Strictly speaking, the year should also be specified in a form consistent
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with localtime(), i.e. the offset from 1900.
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In order to make the interpretation of the year easier for humans,
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however, who are more accustomed to seeing years as two-digit or four-digit
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values, the following conventions are followed:
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=over 4
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=item *
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Years greater than 999 are interpreted as being the actual year,
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rather than the offset from 1900. Thus, 1963 would indicate the year
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Martin Luther King won the Nobel prize, not the year 2863.
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=item *
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Years in the range 100..999 are interpreted as offset from 1900,
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so that 112 indicates 2012. This rule also applies to years less than zero
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(but see note below regarding date range).
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=item *
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Years in the range 0..99 are interpreted as shorthand for years in the
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rolling "current century," defined as 50 years on either side of the current
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year. Thus, today, in 1999, 0 would refer to 2000, and 45 to 2045,
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but 55 would refer to 1955. Twenty years from now, 55 would instead refer
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to 2055. This is messy, but matches the way people currently think about
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two digit dates. Whenever possible, use an absolute four digit year instead.
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=back
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The scheme above allows interpretation of a wide range of dates, particularly
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if 4-digit years are used.
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Please note, however, that the range of dates that can be actually be handled
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depends on the size of an integer (time_t) on a given platform.
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Currently, this is 32 bits for most systems, yielding an approximate range
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from Dec 1901 to Jan 2038.
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Both timelocal() and timegm() croak if given dates outside the supported
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range.
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=head1 IMPLEMENTATION
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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. Note that the timezone is evaluated for
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each date because countries occasionally change their official timezones.
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Assuming that localtime() corrects for these changes, this routine will
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also be correct. The daylight savings offset is currently assumed
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to be one hour.
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=head1 BUGS
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The whole scheme for interpreting two-digit years can be considered a bug.
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Note that the cache currently handles only years from 1900 through 2155.
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The proclivity to croak() is probably a bug.
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=cut
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