This is pretty neat. Thanks! Yeah the swapping of prev and curr seems to be a stumbling block.
On Sunday, February 24, 2013 6:08:39 PM UTC-5, Aria Haghighi wrote: > > I have a solution (gist here https://gist.github.com/aria42/5026109, key > bits pasted below). It's pretty short (15 lines) and readable (I think) and > only 50% slower than the Java version on my machine (averaging over 25 runs > of your benchmark function). > > Generally, I've found it's really easy when you just translate Java code > like this into Clojure, the Clojure will read worse than the original Java; > to boot it will also be slower! And not to be insulting, but I think the > other Clojure solutions I saw in this thread seem to have this property. > You usually have to pull out some abstraction in order to regain on the > readability and concentrate on performance there. Here, I think it's a > macro you'll probably use all over the place, arr-max, which will find the > largest value of an expression looping over an array's index and values. > Then lcs is just nested uses of arr-max that I think is pretty reasonable. > The thing which clutters the remaining code are the prev/cur swapping which > I don't have a slick way of handling. > > (defmacro arr-max > "return maximum value of `expr` over the indices > and values of array `arr`, where `idx-symb` and `val-symb` > are bound to index and values of `arr`" > [arr idx-symb val-symb expr] > `(let [arr# ~arr > n# (alength arr#)] > (loop [~idx-symb 0 max-val# java.lang.Long/MIN_VALUE] > (if (= ~idx-symb n#) > max-val# > (let [~val-symb (aget arr# ~idx-symb) > val# ~expr] > (recur (inc ~idx-symb) > (if (> val# max-val#) > val# max-val#))))))) > > (defn lcs [^objects a1 ^objects a2] > (let [prev-ref (atom (long-array (inc (alength a2)))) > cur-ref (atom (long-array (inc (alength a2))))] > (arr-max a1 i v1 > (let [^longs prev @prev-ref > ^longs cur @cur-ref > max-len (arr-max a2 j v2 > (let [match-len (if (.equals v1 v2) > (inc (aget prev j)) > 0)] > (aset cur (inc j) match-len) > match-len))] > (reset! prev-ref cur) > (reset! cur-ref prev) > (long max-len))))) > > > > On Sunday, February 24, 2013 12:45:18 PM UTC-8, Marko Topolnik wrote: >> >> >> >> On Sunday, February 24, 2013 9:15:45 PM UTC+1, puzzler wrote: >>> >>> >>> As I mentioned before, I'm generally happy with Clojure's performance, >>> but the few times I've had performance problems, I ended up rewriting the >>> code at least three different ways in order to try to find the magic >>> combination that would boost performance. >>> >> >> Lately I've leaned towards going full monty the first time out: stop >> guessing and optimize everything past the entry point to the critical >> section. It sounds like more work up front, but in the end it's the "smart" >> approach that results in more total effort. >> >> >>> Fortunately, dropping down to Java is relatively painless. But I still >>> wonder whether there might be some benefit to having a "low-level DSL" >>> within Clojure, a mode that lets you choose to write your code in a way >>> where the semantics are closer to the underlying platform. >>> >> >> Just one feature would make a huge difference: reassignable locals. >> >> >>> I haven't used Clojurescript much, but I get the impression that >>> Clojurescript is already a step in that direction, with a simpler story >>> regarding how mutation, arrays, and primitives are translated to the >>> underlying platform, arguably making it easier to get good performance when >>> you need it. >>> >> >> The gap between Clojure and JavaScript is far less than Java because both >> are dynamic. I think that plays a big part in why ClojureScript can be more >> transparent. >> >> > -- -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
