On Wed, May 7, 2008 at 11:12 PM, Ben Einstein <[EMAIL PROTECTED]> wrote: > John's suggestion of getting rid of strlen was spot on; the code below works > extremely well if using [NSData length] a single time before the loop. > > What I'm still curious about is the difference in processing between the > NSImage and the zip archive. The same code and the same number of bytes but > orders of magnitude slower. >
Is there still a difference in processing speed after swapping to using the length function? To be honest, I'm with John- the prior code couldn't possibly have been working. I think it's likely that either the images had a null byte very early in their data (not at all surprising) and as such were doing almost no work, or that the zip archives had *no* null bytes and the loop was therefore moving straight on past the end of the archive until it hit a null byte somewhere in memory- the only thing suggesting against this is that I'd have expected the occasional segfault if that were happening. Part of your code appends exactly one byte to an NSData every time through the loop. If the source data is 600k, you're doing 300k calls to append bytes to the NSData object, which is about as inefficient as it's possible to get. I'd strongly suggest grabbing the length of the source data, halving that, malloc()'ing an appropriate-length character array, and then writing the bytes directly into the character array to subsequently be stuck into your output object. (If you wanted to go even fancier you could probably operate on a word at a time - 8 source hex characters - but that may not be necessary after you stop calling appendBytes.) I'm willing to bet that if you sharked right now, that would be your bottleneck. On that note, John suggested sharking in his first response, and your response to him was "I know what's happening, so I don't think Shark or Instruments can help any." I would very strongly suggest that this response is very wrong- a shark session would have very rapidly shown both the strlen call and the appenddata calls to be extreme hotspots in your code, which might have pointed you to the problem. -- - David T. Wilson [EMAIL PROTECTED] _______________________________________________ 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 [EMAIL PROTECTED]
