Date: Tue, 26 Nov 2013 23:25:50 -0500 From: Rich Felker <dalias@...ifal.cx> To: musl@...ts.openwall.com Subject: Re: [PATCH] Add support for leap seconds in zoneinfo files On Wed, Nov 27, 2013 at 04:10:35AM +0000, Laurent Bercot wrote: > > >By the way, this brings me to one part of the proposed patch that I'd > >definitely like to see changed: the pre-parsing the leapseconds data > >and storage in static memory. This both wastes static storage (800 > >bytes for 64-bit systems) and puts an arbitrary limit on the data size > >where it's not needed. I'd really prefer that the leapsecond > >processing happen direct from the mmapped space, just like the way > >time zone transitions are handled. > > Ok, but that will be more invasive. Time zone transitions can all be > performed in __secs_to_zone, but leap second data needs to be available > for __secs_to_tm and __tm_to_secs, since we only want to perform leap > second calculations when converting from/to broken-down time, not when > returning raw seconds: so interface changes will be necessary. __secs_to_tm and __tm_to_secs are not the right places for applying leap seconds, because they affect gmtime, which is specified strictly by POSIX to have a particular relationship with time_t... > >It would also be preferable to use > >a binary search like what's used on the transition list instead of a > >linear search; this change to binary search would probably more than > >compensate for any performance loss from reading directly from the > >mmapped data. > > I don't think it's needed. The leap second table is searched in > descending order, and most calls to time functions are made with the > current time, or something close to it, so a linear search will stop > at the first item in most cases. And the rare worst case is only 25 > iterations for now. I'll change to binary search if you insist, but > I really feel it would add complexity for a very tiny benefit in the > rare case and no performance increase at all in the common case. I'm faily indifferent on it, but I don't think the binary search is significantly more complicated. Rich
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