Time::Local(3) Perl Programmers Reference Guide Time::Local(3)NAMETime::Local - efficiently compute time from local and GMT
time
SYNOPSIS
$time = timelocal($sec,$min,$hours,$mday,$mon,$year);
$time = timegm($sec,$min,$hours,$mday,$mon,$year);
DESCRIPTION
These routines are quite efficient and yet are always
guaranteed to agree with localtime() and gmtime(), the
most notable points being that year is year-1900 and month
is 0..11. We manage this by caching the start times of
any months we've seen before. If we know the start time
of the month, we can always calculate any time within the
month. The start times themselves are guessed by
successive approximation starting at the current time,
since most dates seen in practice are close to the current
date. Unlike algorithms that do a binary search (calling
gmtime once for each bit of the time value, resulting in
32 calls), this algorithm calls it at most 6 times, and
usually only once or twice. If you hit the month cache,
of course, it doesn't call it at all.
timelocal is implemented using the same cache. We just
assume that we're translating a GMT time, and then fudge
it when we're done for the timezone and daylight savings
arguments. The timezone is determined by examining the
result of localtime(0) when the package is initialized.
The daylight savings offset is currently assumed to be one
hour.
Both routines return -1 if the integer limit is hit. I.e.
for dates after the 1st of January, 2038 on most machines.
16/Sep/1999 perl 5.005, patch 03 1
