Thanks :) I will make the conversion to CC_LONG to be more clear, but about the bug, I mean it will be impossible to happen on this case, since the max length will be always 64kb :)
About the remote thing, I mean its more low level things, the HD is just mounted as an Volume (on /Volumes/Wilker-1), so, I mean the handling on this case should be transparent, the low level drivers should take care of it :) I learned a lot from this thread, thanks :) --- Wilker Lúcio http://about.me/wilkerlucio/bio Kajabi Consultant +55 81 82556600 On Wed, Jun 29, 2011 at 5:31 PM, Quincey Morris <quinceymor...@earthlink.net > wrote: > On Jun 29, 2011, at 12:26, Wilker wrote: > > > +(NSString *)generateHashFromPath:(NSString *)path { > > const NSUInteger CHUNK_SIZE = 65536; > > > > NSError *error = nil; > > NSData *fileData = [NSData dataWithContentsOfFile:path > options:NSDataReadingMapped | NSDataReadingUncached error:&error]; > > > > if (error) { > > return nil; > > } > > > > const uint8_t* buffer = [fileData bytes]; > > > > NSUInteger byteLength = [fileData length]; > > NSUInteger byteOffset = 0; > > > > if (byteLength > CHUNK_SIZE) { > > byteOffset = byteLength - CHUNK_SIZE; > > byteLength = CHUNK_SIZE; > > } > > > > CC_MD5_CTX md5; > > CC_MD5_Init(&md5); > > > > CC_MD5_Update(&md5, buffer, (unsigned int) byteLength); > > CC_MD5_Update(&md5, buffer + byteOffset, (unsigned int) byteLength); > > > > unsigned char digest[CC_MD5_DIGEST_LENGTH]; > > > > CC_MD5_Final(digest, &md5); > > > > NSMutableString *ret = [NSMutableString > stringWithCapacity:CC_MD5_DIGEST_LENGTH * 2]; > > > > for (int i = 0; i < CC_MD5_DIGEST_LENGTH; i++) { > > [ret appendFormat:@"%02x", digest[i]]; > > } > > > > return [ret lowercaseString]; > > } > > This looks good to me, but since we're noodling around various topics here, > let me nitpick at some details: > > 1. Format specifier '%x' produces lower case letters, so you don't need to > lowercase the returned string. If you'd happened to want uppercase, there's > '%X'. > > If you're just trying to return an immutable string, there are three > possible answers: > > a. Don't bother. It's almost always fine to return a NSMutableString when > your method's API's return type says NSString. > > b. Return '[ret copy]'. That allows NSString to do the fastest copy of the > character data that it's capable of. The result is an immutable string. > > c. Go back to the way you first did it, where you spelled out the entire > format string, so you don't ever create a NSMutableString. > > 2. There still a flashing danger signal in your code. Pretty much any time > you have to cast a scalar type, your code gets smelly ( > http://en.wikipedia.org/wiki/Code_smell). > > If you consult the CC_MD5 man page, you'll see that the length parameter > type is officially CC_LONG. What happens if byteLength is bigger than the > largest possible CC_LONG? (In other words, what happens if your file is > bigger than 4GB?) > > WIth this code, the consequences would not be catastrophic, but the wrong > digest would likely be calculated. > > So, declare 'byteLength' as type CC_LONG and get rid of those ad hoc casts. > You might still need a cast, but pair it with a safety check: > > CC_LONG byteLength = (CC_LONG) ([file length] > CHUNK_SIZE ? > CHUNK_SIZE : [file length]); > > That messes up the setting of byteOffset, so you need to change that to > something like: > > NSUInteger byteOffset = [file length] > CHUNK_SIZE ? [file length] - > CHUNK_SIZE : 0; > > Depending on your aesthetic tastes, you might actually want to do: > > NSUInteger fileLength = [fileData length]; > CC_LONG byteLength = (CC_LONG) (fileLength > CHUNK_SIZE ? CHUNK_SIZE > : fileLength); > NSUInteger byteOffset = fileLength > CHUNK_SIZE ? fileLength - > CHUNK_SIZE : 0; > > Anyone reading your code can now see that the cast is harmless, because > you've explicitly checked for the error condition. > > > I tried it against a video of 8.5GB, stored on external drive (at wifi > with Airport Extreme), and it's blazing fast :) > > This is a remarkable statement, if you think about it. My pitch for > 'NSDataReadingMapped' relied on the assumption that the file was local. If > NSData is really providing the effect of memory mapping with a remote file, > it's really doing a *lot* of heavy lifting for you. > > That's really quite a surprising result. > > > > > _______________________________________________ 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
