Note that looping with primitive int is faster than with long, and native array functions accepts/returns int instead of long for their index and length.
It is very hard to eliminate boxing without dropping to java. In you example, calling bit-xor does 2 autoboxing (and 1 long to int cast as aset-byte takes int index), as there is no byte variant of clojure.lang.Numbers/xor. Also you cannot detect it without advanced profiler or bytecode analysis. Best, Jozef On Thu, Mar 13, 2014 at 1:34 PM, Alex Miller <a...@puredanger.com> wrote: > Agreed with all the comments on this so far. I would also say that dotimes > is slower than loop for stuff like this so I would also make that change. > > (defn inplace-xor [^bytes a ^bytes b ^bytes out] > (let [len (alength a)] > (loop [i 0] > (when (< i len) > (aset-byte out i (bit-xor (aget a i) (aget b i))) > (recur (inc i)))))) > > In this scenario loop/recur will use a primitive long for i. And then I > would look at the bytecode to verify no boxing is occurring. > > On Thursday, March 13, 2014 3:36:14 AM UTC-5, Michael Gardner wrote: >> >> Might be slow because of the polymorphic nature of nth. If you replace >> nth with aget (and turn on *warn-on-reflection*, which is a good idea when >> performance-tuning), you'll get reflection warnings because Clojure doesn't >> know what Java method to use since it doesn't know what type of objects a >> and b are. Once you silence those with type hints like in Walter's example, >> you get roughly a 2x speedup (in my tests). >> >> BTW, I'd write it like this: >> >> (defn inplace-xor [^bytes a ^bytes b ^bytes out] >> (dotimes [i (alength a)] >> (aset-byte out i >> (bit-xor (aget a i) (aget b i))))) >> > > >> >> On Mar 13, 2014, at 00:26 , Ignacio Corderi <icor...@soe.ucsc.edu> >> wrote: >> >> > Hey guys, here is a huge performance problem I'm trying to figure out: >> > >> > ;; Say you have 2 data arrays sitting out there of 1 MB >> > >> > (def one-mb (byte-array (* 1024 1024))) >> > (def another-mb (byte-array (* 1024 1024))) >> > >> > ;; and another one that should have the byte-by-byte XOR of the >> previous two >> > >> > (def out-mb (byte-array (* 1024 1024))) >> > >> > ;; question is... how do you code this guy, so that it doesn't take >> forever >> > >> > (defn inplace-xor [a b out] >> > (def ln (count a)) >> > (loop [x 0] >> > (if (< x ln) >> > (do >> > (aset-byte out x (bit-xor (nth a x) (nth b x))) >> > (recur (+ x 1)) >> > )))) >> > >> > ;; checking the time >> > >> > (time (inplace-xor one-mb another-mb out-mb)) >> > >> > ;; takes about ~400ms which is.... well... A LOT >> > >> > ;; I'm happy to receive a solution that involves calling some java >> library... >> > >> > Thanks in advance! >> > -Ignacio >> > >> > >> > >> > -- >> > You received this message because you are subscribed to the Google >> > Groups "Clojure" group. >> > To post to this group, send email to clo...@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+u...@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+u...@googlegroups.com. >> > For more options, visit https://groups.google.com/d/optout. >> >> >> -- > 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/d/optout. > -- 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/d/optout.
