Time::Local(3) Time::Local(3)
Time::Local - efficiently compute time from local and GMT time
$time = timelocal($sec,$min,$hours,$mday,$mon,$year);
$time = timegm($sec,$min,$hours,$mday,$mon,$year);
These routines are quite efficient and yet are always guaranteed to agree
with localtime() and gmtime(). 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.
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