On Mon, Apr 6, 2009 at 1:55 AM, Greg Guerin <glgue...@amug.org> wrote: > Michael Ash wrote: > >> Good point. Although this has the disadvantage of temporarily using a >> bunch of memory, roughly doubling your footprint for this data >> structure, that's not likely to be a problem for the typical use cases >> for this thing. > > I don't see why it should take extra memory. > > As you say, there will be a larger NSData footprint, roughly double, if a > single NSMutableData is used to accumulate all the individual NSData's, and > that NSMutableData is then hashed as the final step. However, I know of no > requirement to do it that way. > > A secure-hash algorithm can usually be called incrementally. Each object to > be hashed returns its NSData, and that chunk of bytes is then digested into > the cumulative secure-hash value. Any blocking needed by the hash is > typically done internal to the hash algorithm itself. Even if the series of > objects represented by an NSArray or NSDictionary were evaluated using > simple traversal, there's still only a need for one NSData from one > primitive object at a time. And you can put an autorelease pool at any > level of the traversal, should it seem prudent. > > For example, see the openssl functions SHA1_Init(), SHA1_Update(), and > SHA1_Final(), as contrasted to the monolithic SHA1() function. This is not > unique to SHA1, either; most digests work this way. > > Or am I missing something?
Just that I assumed from context that your proposed gc_canonicalData method would be recursive like this one, providing a single chunk at the end. You certainly could use incremental updating instead, but you're going to need a different architecture to do it, since you need to run the update code for each leaf of your tree. Mike _______________________________________________ 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: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
