timelocal.pl revision 290001 
1;# timelocal.pl
2;#
3;# Usage:
4;#	$time = timelocal($sec,$min,$hours,$mday,$mon,$year,$junk,$junk,$isdst);
5;#	$time = timegm($sec,$min,$hours,$mday,$mon,$year);
6
7;# These routines are quite efficient and yet are always guaranteed to agree
8;# with localtime() and gmtime().  We manage this by caching the start times
9;# of any months we've seen before.  If we know the start time of the month,
10;# we can always calculate any time within the month.  The start times
11;# themselves are guessed by successive approximation starting at the
12;# current time, since most dates seen in practice are close to the
13;# current date.  Unlike algorithms that do a binary search (calling gmtime
14;# once for each bit of the time value, resulting in 32 calls), this algorithm
15;# calls it at most 6 times, and usually only once or twice.  If you hit
16;# the month cache, of course, it doesn't call it at all.
17
18;# timelocal is implemented using the same cache.  We just assume that we're
19;# translating a GMT time, and then fudge it when we're done for the timezone
20;# and daylight savings arguments.  The timezone is determined by examining
21;# the result of localtime(0) when the package is initialized.  The daylight
22;# savings offset is currently assumed to be one hour.
23
24CONFIG: {
25    package timelocal;
26
27    @epoch = localtime(0);
28    $tzmin = $epoch[2] * 60 + $epoch[1];	# minutes east of GMT
29    if ($tzmin > 0) {
30	$tzmin = 24 * 60 - $tzmin;		# minutes west of GMT
31	$tzmin -= 24 * 60 if $epoch[5] == 70;	# account for the date line
32    }
33
34    $SEC = 1;
35    $MIN = 60 * $SEC;
36    $HR = 60 * $MIN;
37    $DAYS = 24 * $HR;
38    $YearFix = ((gmtime(946684800))[5] == 100) ? 100 : 0;
39}
40
41sub timegm {
42    package timelocal;
43
44    $ym = pack(C2, @_[5,4]);
45    $cheat = $cheat{$ym} || &cheat;
46    $cheat + $_[0] * $SEC + $_[1] * $MIN + $_[2] * $HR + ($_[3]-1) * $DAYS;
47}
48
49sub timelocal {
50    package timelocal;
51
52    $ym = pack(C2, @_[5,4]);
53    $cheat = $cheat{$ym} || &cheat;
54    $cheat + $_[0] * $SEC + $_[1] * $MIN + $_[2] * $HR + ($_[3]-1) * $DAYS
55	+ $tzmin * $MIN - 60 * 60 * ($_[8] != 0);
56}
57
58package timelocal;
59
60sub cheat {
61    $year = $_[5];
62    $month = $_[4];
63    $guess = $^T;
64    @g = gmtime($guess);
65    $year += $YearFix if $year < $epoch[5];
66    while ($diff = $year - $g[5]) {
67	$guess += $diff * (364 * $DAYS);
68	@g = gmtime($guess);
69    }
70    while ($diff = $month - $g[4]) {
71	$guess += $diff * (28 * $DAYS);
72	@g = gmtime($guess);
73    }
74    $g[3]--;
75    $guess -= $g[0] * $SEC + $g[1] * $MIN + $g[2] * $HR + $g[3] * $DAYS;
76    $cheat{$ym} = $guess;
77}
78