$time = timelocal($sec,$min,$hours,$mday,$mon,$year);
$time = timegm($sec,$min,$hours,$mday,$mon,$year);
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 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.