I'll bet the atom accesses dominate the computation. They are a part of
Clojures software transactional memory (STM) and have a cost.
Something like this (untested) should be faster:
(->> (iterate neighbors #{p}) (drop 1999) first)
neighbors could be:
(into #{} (for [[id jd] [[-1 0] [+1 0] [0 +1] [0 -1]]
[(+ i id) (+ j jd)]))
This creates some negligible lazy lists.
If you want to test actual time for hash inserts, though, you'll probably
need to use transients or some such, and the code would become less
idiomatic.
On Tue, Nov 15, 2016 at 10:39 PM, Didier <didi...@gmail.com> wrote:
> Hey all,
>
> I came upon a benchmark of F#, Rust and OCaml, where F# performs much
> faster then the other two. I decided for fun to try and port it to Clojure
> to see how Clojure does. Benchmark link: https://github.com/c-cube/
> hashset_benchs
>
> This is my code for it: https://gist.github.com/didibus/
> 1fd4c00b69d927745fbce3dcd7ca461a
>
> (ns hash-set-bench
> "A Benchmark I modified to Clojure from:
> https://github.com/c-cube/hashset_benchs";)
>
> (defn iterNeighbors [f [i j]]
> (f [(dec i) j])
> (f [(inc i) j])
> (f [i (dec j)])
> (f [i (inc j)]))
>
> (defn nth* [n p]
> (loop [n n s1 #{p} s2 #{}]
> (if (= n 0)
> s1
> (let [s0 (atom #{})]
> (letfn [(add [p]
> (when (not (or (contains? s1 p) (contains? s2 p)))
> (reset! s0 (conj @s0 p))))]
> (doseq [p s1] (iterNeighbors add p))
> (recur (dec n) @s0 s1))))))
>
> #_(printf "result is %d" (count (time (nth* 2000 [0 0]))))
>
> And here's the F# code: https://github.com/c-cube/
> hashset_benchs/blob/master/neighbors2.fsx
>
> Currently, this takes about 30s in Clojure, while it only takes around 3s
> for OCaml, Rust and F#.
>
> From what I see, the differences between my code and theirs are:
>
> - Lack of a Point struct, I'm just using a vector.
> - They use a mutable set, I don't.
> - They overrode Hashing for their point struct, as well as equality. I
> rely on Clojure's default hashing, and vector equality.
>
> I'm not sure if any of these things should really impact performance that
> much though. And what I could do in Clojure if I wanted to improve it.
>
>
> Any Help?
>
>
> Thanks.
>
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