On Feb 3, 3:54 pm, "Shen, Feng" <[email protected]> wrote:
> > I was able to shave off some more by writing (not= 0 (rem i d)) as (<
>
> 0 (rem i d)).
>
> the running time is about 4787ms on my computer, compare to *2759ms *of the
> java version, a bit slower, but not much.
>
> 沈锋
> 美味书签 :http://meiweisq.com
> 博客：http://shenfeng.me
>
> On Sun, Feb 3, 2013 at 6:42 PM, Shantanu Kumar
> <[email protected]>wrote:
>
>
>
>
>
>
>
>
>
> > On Feb 3, 12:54 pm, Curtis Gagliardi <[email protected]>
> > wrote:
> > > I took your version Feng and used rem instead of mod and added a type
> > hint
> > > and got down from:
> > > 23217.321626 => 11398.389942
>
> > > No idea where to go from here though. I'm surprised there's such a
> > > difference even not using any sort of collection.
>
> > > (defn smallest-multiple-of-1-to-n-hinted-rem
> > > [^long n]
> > > (loop [i n]
> > > (if (loop [d 2]
> > > (cond (> d n) true
> > > (not= 0 (rem i d)) false
> > > :else (recur (inc d))))
> > > i
> > > (recur (inc i))))
>
> > I was able to shave off some more by writing (not= 0 (rem i d)) as (<
> > 0 (rem i d)).
For some reason, by splitting out the inner loop into a function
shaved 6 more seconds (from 34s to 28s) on my low-config 32-bit
laptop:
(defn every-d?
[^long x ^long n]
(loop [d 2]
(cond (> d n) true
(< 0 (rem x d)) false
:otherwise (recur (inc d)))))
(defn smallest-multiple-of-1-to-n
[n]
(let [n (long n)]
(loop [x n]
(if (every-d? x n)
x
(recur (inc x))))))
Changing (< 0 ...) to (pos? ..) had no noticeable delay. This is of
course only a micro-benchmark and numbers would probably change when
the JIT compiler kicks in.
With *unchecked-math* set to true, the Clojure version above takes
28s. Interestingly, when I modified the Java version to use Long, the
time went up from 18s to 40s and for unboxed long, the time went up
from 18s to 37s.
Shantanu
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