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lib/Time/Local.pm
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a0d0e21e 1package Time::Local;
396e3838 2require 5.6.0;
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3require Exporter;
4use Carp;
b75c8c73 5use strict;
a0d0e21e 6
396e3838 7our $VERSION = '1.02';
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8our @ISA = qw( Exporter );
9our @EXPORT = qw( timegm timelocal );
10our @EXPORT_OK = qw( timegm_nocheck timelocal_nocheck );
a0d0e21e 11
06ef4121 12# Set up constants
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13our $SEC = 1;
14our $MIN = 60 * $SEC;
15our $HR = 60 * $MIN;
16our $DAY = 24 * $HR;
06ef4121 17# Determine breakpoint for rolling century
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18 my $ThisYear = (localtime())[5];
19 my $NextCentury = int($ThisYear / 100) * 100;
20 my $Breakpoint = ($ThisYear + 50) % 100;
21 $NextCentury += 100 if $Breakpoint < 50;
9bb8015a 22
b75c8c73 23our(%Options, %Cheat);
e36f48eb 24
9bb8015a 25sub timegm {
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26 my (@date) = @_;
27 if ($date[5] > 999) {
28 $date[5] -= 1900;
29 }
30 elsif ($date[5] >= 0 && $date[5] < 100) {
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31 $date[5] -= 100 if $date[5] > $Breakpoint;
32 $date[5] += $NextCentury;
06ef4121 33 }
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34 my $ym = pack('C2', @date[5,4]);
35 my $cheat = $Cheat{$ym} || &cheat($ym, @date);
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36 $cheat
37 + $date[0] * $SEC
38 + $date[1] * $MIN
39 + $date[2] * $HR
40 + ($date[3]-1) * $DAY;
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41}
42
e36f48eb 43sub timegm_nocheck {
b75c8c73 44 local $Options{no_range_check} = 1;
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45 &timegm;
46}
47
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48sub timelocal {
49 my $t = &timegm;
84902520 50 my $tt = $t;
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51
52 my (@lt) = localtime($t);
53 my (@gt) = gmtime($t);
84902520 54 if ($t < $DAY and ($lt[5] >= 70 or $gt[5] >= 70 )) {
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55 # Wrap error, too early a date
56 # Try a safer date
e85ca32b 57 $tt += $DAY;
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58 @lt = localtime($tt);
59 @gt = gmtime($tt);
84902520 60 }
a0d0e21e 61
9bb8015a 62 my $tzsec = ($gt[1] - $lt[1]) * $MIN + ($gt[2] - $lt[2]) * $HR;
16bb4654 63
16bb4654 64 if($lt[5] > $gt[5]) {
65 $tzsec -= $DAY;
66 }
67 elsif($gt[5] > $lt[5]) {
68 $tzsec += $DAY;
69 }
70 else {
71 $tzsec += ($gt[7] - $lt[7]) * $DAY;
72 }
73
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74 $tzsec += $HR if($lt[8]);
75
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76 my $time = $t + $tzsec;
77 my @test = localtime($time + ($tt - $t));
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78 $time -= $HR if $test[2] != $_[2];
79 $time;
80}
81
e36f48eb 82sub timelocal_nocheck {
b75c8c73 83 local $Options{no_range_check} = 1;
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84 &timelocal;
85}
86
a0d0e21e 87sub cheat {
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88 my($ym, @date) = @_;
89 my($sec, $min, $hour, $day, $month, $year) = @date;
90 unless ($Options{no_range_check}) {
eee32007 91 croak "Month '$month' out of range 0..11" if $month > 11 || $month < 0;
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92 my $md = (31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31)[$month];
93 $md++ if $month == 1 &&
94 $year % 4 == 0 && ($year % 100 > 0 || $year % 400 == 100); # leap
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95 croak "Day '$day' out of range 1..$md" if $day > $md || $day < 1;
96 croak "Hour '$hour' out of range 0..23" if $hour > 23 || $hour < 0;
97 croak "Minute '$min' out of range 0..59" if $min > 59 || $min < 0;
98 croak "Second '$sec' out of range 0..59" if $sec > 59 || $sec < 0;
ac54365a 99 }
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100 my $guess = $^T;
101 my @g = gmtime($guess);
102 my $lastguess = "";
103 my $counter = 0;
104 while (my $diff = $year - $g[5]) {
105 my $thisguess;
106 croak "Can't handle date (".join(", ",@date).")" if ++$counter > 255;
16bb4654 107 $guess += $diff * (363 * $DAY);
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108 @g = gmtime($guess);
109 if (($thisguess = "@g") eq $lastguess){
b75c8c73 110 croak "Can't handle date (".join(", ",@date).")";
06ef4121 111 #date beyond this machine's integer limit
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112 }
113 $lastguess = $thisguess;
114 }
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115 while (my $diff = $month - $g[4]) {
116 my $thisguess;
117 croak "Can't handle date (".join(", ",@date).")" if ++$counter > 255;
16bb4654 118 $guess += $diff * (27 * $DAY);
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119 @g = gmtime($guess);
120 if (($thisguess = "@g") eq $lastguess){
b75c8c73 121 croak "Can't handle date (".join(", ",@date).")";
06ef4121 122 #date beyond this machine's integer limit
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123 }
124 $lastguess = $thisguess;
125 }
b75c8c73 126 my @gfake = gmtime($guess-1); #still being sceptic
a0d0e21e 127 if ("@gfake" eq $lastguess){
b75c8c73 128 croak "Can't handle date (".join(", ",@date).")";
06ef4121 129 #date beyond this machine's integer limit
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130 }
131 $g[3]--;
16bb4654 132 $guess -= $g[0] * $SEC + $g[1] * $MIN + $g[2] * $HR + $g[3] * $DAY;
b75c8c73 133 $Cheat{$ym} = $guess;
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134}
135
1361;
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137
138__END__
139
140=head1 NAME
141
142Time::Local - efficiently compute time from local and GMT time
143
144=head1 SYNOPSIS
145
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146 $time = timelocal($sec,$min,$hour,$mday,$mon,$year);
147 $time = timegm($sec,$min,$hour,$mday,$mon,$year);
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148
149=head1 DESCRIPTION
150
396e3838 151These routines are the inverse of built-in perl functions localtime()
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152and gmtime(). They accept a date as a six-element array, and return
153the corresponding time(2) value in seconds since the Epoch (Midnight,
154January 1, 1970). This value can be positive or negative.
155
156It is worth drawing particular attention to the expected ranges for
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157the values provided. The value for the day of the month is the actual day
158(ie 1..31), while the month is the number of months since January (0..11).
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159This is consistent with the values returned from localtime() and gmtime().
160
e36f48eb 161The timelocal() and timegm() functions perform range checking on the
396e3838 162input $sec, $min, $hour, $mday, and $mon values by default. If you'd
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163rather they didn't, you can explicitly import the timelocal_nocheck()
164and timegm_nocheck() functions.
ac54365a 165
e36f48eb 166 use Time::Local 'timelocal_nocheck';
3cb6de81 167
a1f33342 168 {
a1f33342 169 # The 365th day of 1999
e36f48eb 170 print scalar localtime timelocal_nocheck 0,0,0,365,0,99;
ac54365a 171
a1f33342 172 # The twenty thousandth day since 1970
e36f48eb 173 print scalar localtime timelocal_nocheck 0,0,0,20000,0,70;
ac54365a 174
a1f33342 175 # And even the 10,000,000th second since 1999!
e36f48eb 176 print scalar localtime timelocal_nocheck 10000000,0,0,1,0,99;
a1f33342 177 }
ac54365a 178
e36f48eb 179Your mileage may vary when trying these with minutes and hours,
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180and it doesn't work at all for months.
181
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182Strictly speaking, the year should also be specified in a form consistent
183with localtime(), i.e. the offset from 1900.
184In order to make the interpretation of the year easier for humans,
185however, who are more accustomed to seeing years as two-digit or four-digit
186values, the following conventions are followed:
187
188=over 4
189
190=item *
191
192Years greater than 999 are interpreted as being the actual year,
193rather than the offset from 1900. Thus, 1963 would indicate the year
90ca0aaa 194Martin Luther King won the Nobel prize, not the year 2863.
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195
196=item *
197
198Years in the range 100..999 are interpreted as offset from 1900,
199so that 112 indicates 2012. This rule also applies to years less than zero
200(but see note below regarding date range).
201
202=item *
203
204Years in the range 0..99 are interpreted as shorthand for years in the
205rolling "current century," defined as 50 years on either side of the current
206year. Thus, today, in 1999, 0 would refer to 2000, and 45 to 2045,
207but 55 would refer to 1955. Twenty years from now, 55 would instead refer
208to 2055. This is messy, but matches the way people currently think about
209two digit dates. Whenever possible, use an absolute four digit year instead.
210
211=back
212
213The scheme above allows interpretation of a wide range of dates, particularly
214if 4-digit years are used.
90ca0aaa 215
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216Please note, however, that the range of dates that can be actually be handled
217depends on the size of an integer (time_t) on a given platform.
218Currently, this is 32 bits for most systems, yielding an approximate range
219from Dec 1901 to Jan 2038.
220
221Both timelocal() and timegm() croak if given dates outside the supported
222range.
223
224=head1 IMPLEMENTATION
225
226These routines are quite efficient and yet are always guaranteed to agree
227with localtime() and gmtime(). We manage this by caching the start times
228of any months we've seen before. If we know the start time of the month,
229we can always calculate any time within the month. The start times
230themselves are guessed by successive approximation starting at the
231current time, since most dates seen in practice are close to the
232current date. Unlike algorithms that do a binary search (calling gmtime
233once for each bit of the time value, resulting in 32 calls), this algorithm
234calls it at most 6 times, and usually only once or twice. If you hit
235the month cache, of course, it doesn't call it at all.
236
237timelocal() is implemented using the same cache. We just assume that we're
238translating a GMT time, and then fudge it when we're done for the timezone
239and daylight savings arguments. Note that the timezone is evaluated for
240each date because countries occasionally change their official timezones.
241Assuming that localtime() corrects for these changes, this routine will
242also be correct. The daylight savings offset is currently assumed
243to be one hour.
244
245=head1 BUGS
246
247The whole scheme for interpreting two-digit years can be considered a bug.
248
249Note that the cache currently handles only years from 1900 through 2155.
250
251The proclivity to croak() is probably a bug.
252
253=cut