For some AVM1 and AVM2 flash representation of objects, fire up this breeze presentation about the flash player 9.
http://seminars.breezecentral.com/p64058844/ Around minute 28 into the presentation, it talks about AVM1 and AVM2 representation of an object. Like I suspected, AVM1 uses a straight hash table. B. 2006/5/16, Ron Wheeler <[EMAIL PROTECTED]>:
Bernard Poulin wrote: >> If you can not tune a HashMap it will be worse than an ordinary array. >> It will take more space and more processing time. > > This will of course depend on the size and usage - it *may* be more > efficient with hashmaps. Do you really think we can generalize being it > worse all the time? > I will not be far wrong. If your primary allocation is to small, many array keys hash to the same spot and you have to search a long linked list. It is is too big, you waste a lot of space. It is not trivial to increase the size of the allocation dynamically since you must rehash all of the entries. > Keeping an array "ordered" to be able to do binary searches can > statistically cost a lot of "copying" at insertion time. You are only adjusting links unless you want a balanced tree. > Binary searches may involves a lot more string comparison. In a binary > search comparing the "string hash" value is of no use to know if the > value > is "greater" or "lower" (to decide for the next search direction). In > hashmaps, the lookup in the "chain" after the hash jump can, most of the > time, "skip" a string entry without even looking at the characters by > comparing the 32bit integer hashes. String hashes are only useful for looking up a specific value. It is unlikely that the hashes are even stored since once you store the key/value you no longer have any need for the hash since the position in the main table is known and you can follow the links in the overflow back to the main table(usually). If you are hashed into the overflow, you have to examine each key since the hashes are identical for everyone in the list (otherwise they would not be in the list - they would be in another list of collided hashes). > > About Arrays (this is more than slightly OT) :-) > > I still believe Arrays are implemented as associative arrays. But this is > just pure belief since I have no proof and it could easily change from > one > version of the VM to the other. > "Associative array" is not a physical description of the implementation. It describes the logical way that an Actionscript programmer finds the value associated with a key. The implementation of Array probably involves a fairly simple linked list of key objects that point to value objects. Whether the keys are linked as a tree structure to speed up access is an interesting question which was raised earlier. > var a:Array; > a[0] = 'abc'; > a[123456789] = 'high index value'; > a["this is text"] = 'non-integer index'; > > trace(a.length); /// should output 123456790 > > Sidenote: I often use this "feature" of Arrays to make an "ordered > associative array" in one single object. This may look a bit like a > hack - > but it is perfectly valid. I can both traverse the keys in a fixed custom > order and lookup one item with its key directly. Also you can retrieve > quickly how many items there are using "length". For example, when > inserting > a new entry, I do something like: > > a[key] = value; > a[a.length] = key; > > I would really like to have insights into the flash VM implementation > so I > could do better choices regarding maps and arrays. > Agreed > regards, > B. > > (--snip------rest of previous mail removed to keep it > shorter-------snip---) > _______________________________________________ [email protected] To change your subscription options or search the archive: http://chattyfig.figleaf.com/mailman/listinfo/flashcoders Brought to you by Fig Leaf Software Premier Authorized Adobe Consulting and Training http://www.figleaf.com http://training.figleaf.com
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