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perl 5.000
[perl5.git] / lib / Time / Local.pm
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a0d0e21e
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1package Time::Local;
2require 5.000;
3require Exporter;
4use Carp;
5
6@ISA = qw(Exporter);
7@EXPORT = qw(timegm timelocal);
8
9# timelocal.pl
10#
11# Usage:
12# $time = timelocal($sec,$min,$hours,$mday,$mon,$year);
13# $time = timegm($sec,$min,$hours,$mday,$mon,$year);
14
15# These routines are quite efficient and yet are always guaranteed to agree
16# with localtime() and gmtime(). We manage this by caching the start times
17# of any months we've seen before. If we know the start time of the month,
18# we can always calculate any time within the month. The start times
19# themselves are guessed by successive approximation starting at the
20# current time, since most dates seen in practice are close to the
21# current date. Unlike algorithms that do a binary search (calling gmtime
22# once for each bit of the time value, resulting in 32 calls), this algorithm
23# calls it at most 6 times, and usually only once or twice. If you hit
24# the month cache, of course, it doesn't call it at all.
25
26# timelocal is implemented using the same cache. We just assume that we're
27# translating a GMT time, and then fudge it when we're done for the timezone
28# and daylight savings arguments. The timezone is determined by examining
29# the result of localtime(0) when the package is initialized. The daylight
30# savings offset is currently assumed to be one hour.
31
32# Both routines return -1 if the integer limit is hit. I.e. for dates
33# after the 1st of January, 2038 on most machines.
34
35@epoch = localtime(0);
36$tzmin = $epoch[2] * 60 + $epoch[1]; # minutes east of GMT
37if ($tzmin > 0) {
38 $tzmin = 24 * 60 - $tzmin; # minutes west of GMT
39 $tzmin -= 24 * 60 if $epoch[5] == 70; # account for the date line
40}
41
42$SEC = 1;
43$MIN = 60 * $SEC;
44$HR = 60 * $MIN;
45$DAYS = 24 * $HR;
46$YearFix = ((gmtime(946684800))[5] == 100) ? 100 : 0;
47
48sub timegm {
49 $ym = pack(C2, @_[5,4]);
50 $cheat = $cheat{$ym} || &cheat;
51 return -1 if $cheat<0;
52 $cheat + $_[0] * $SEC + $_[1] * $MIN + $_[2] * $HR + ($_[3]-1) * $DAYS;
53}
54
55sub timelocal {
56 $time = &timegm + $tzmin*$MIN;
57 return -1 if $cheat<0;
58 @test = localtime($time);
59 $time -= $HR if $test[2] != $_[2];
60 $time;
61}
62
63sub cheat {
64 $year = $_[5];
65 $month = $_[4];
66 croak "Month out of range 0..11 in timelocal.pl"
67 if $month > 11 || $month < 0;
68 croak "Day out of range 1..31 in timelocal.pl"
69 if $_[3] > 31 || $_[3] < 1;
70 croak "Hour out of range 0..23 in timelocal.pl"
71 if $_[2] > 23 || $_[2] < 0;
72 croak "Minute out of range 0..59 in timelocal.pl"
73 if $_[1] > 59 || $_[1] < 0;
74 croak "Second out of range 0..59 in timelocal.pl"
75 if $_[0] > 59 || $_[0] < 0;
76 $guess = $^T;
77 @g = gmtime($guess);
78 $year += $YearFix if $year < $epoch[5];
79 $lastguess = "";
80 while ($diff = $year - $g[5]) {
81 $guess += $diff * (363 * $DAYS);
82 @g = gmtime($guess);
83 if (($thisguess = "@g") eq $lastguess){
84 return -1; #date beyond this machine's integer limit
85 }
86 $lastguess = $thisguess;
87 }
88 while ($diff = $month - $g[4]) {
89 $guess += $diff * (27 * $DAYS);
90 @g = gmtime($guess);
91 if (($thisguess = "@g") eq $lastguess){
92 return -1; #date beyond this machine's integer limit
93 }
94 $lastguess = $thisguess;
95 }
96 @gfake = gmtime($guess-1); #still being sceptic
97 if ("@gfake" eq $lastguess){
98 return -1; #date beyond this machine's integer limit
99 }
100 $g[3]--;
101 $guess -= $g[0] * $SEC + $g[1] * $MIN + $g[2] * $HR + $g[3] * $DAYS;
102 $cheat{$ym} = $guess;
103}
104
1051;