Le 9 sept. 2013 à 18:11, Jens Alfke <j...@mooseyard.com> a écrit :
> Parsing dates from strings can be surprisingly expensive — more than once > I’ve seen it show up as the primary hot-spot in code that reads files or > parses network data. NSDateFormatter is very flexible, but you pay for that > in speed. If you only need to parse a single simple date/time format you can > do a lot better. > > A couple of days ago Anrurag Mishra wrote a blog post[1] demonstrating that > you can get about 14x faster performance (yes, 14 *times* faster) by calling > SQLite’s built-in strftime function. (Actually, my experience is that it’s > 30x faster, but I was probably running on different hardware. YMMV.) His code > simply compiles and runs a SQL “SELECT” statement that calls strftime — I > decided to do better than that by extracting the C code from SQLite that does > the actual parsing, and making a direct API for it. That about doubles > performance again. Here are some benchmark results (run on a 2012 MacBook > Pro): > > [fg160,160,160;16:34:40.488| [fg0,128,0;[;NSDateFormatter took 26.97 µsec > [fg160,160,160;16:34:42.709| [fg0,128,0;[;sqlite3 strftime took 0.89 > µsec (30x) > [fg160,160,160;16:34:46.788| [fg0,128,0;[;-dateWithJSONObject took 0.68 > µsec (40x) > [fg160,160,160;16:34:48.649| [fg0,128,0;[;CBLParseDate took 0.47 > µsec (58x) > > (Here CBLParseDate is the raw function that returns a UNIX timestamp, and > -dateWithJSONObject is a wrapper method that returns the same time as an > NSDate object, which of course has extra overhead.) > > Now, the tradeoff is that the optimized code parses only ISO 8601 dates — > this is the informal standard used with JSON, so it’s become really common. > It looks like “2013-09-09T17:52:12Z”. It’s certainly possible to munge this > code to parse a slightly different format, but you’re on your own there! > > You can grab my code (which is just a hack-and-slash of Richard Hipp’s SQLite > code) from the Couchbase Lite repo[2]. It has no dependencies on anything but > the C standard library, so it should be easy to drop into your own projects. > Isn't it possible to parse it using the libc function strftime ? How does it compare to the other solutions ? -- Jean-Daniel _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
