Using unchecked-remainder and adding a type declaration to the last
constant keeps the primitives unboxed and improves performance by a
factor of 6 for me. I couldn't say whether there's a reason rem and
mod don't work like you'd expect here.
(defn NF-mod-limit [p q limit]
(let [p (long p) q (long q) limit (long limit)]
(loop [n (long 0), nf (long 0), z (long 0), S (long 290797)]
(if (= n (inc q))
nf
(recur
(inc n)
(unchecked-remainder
(+ nf (* (unchecked-remainder S p) z))
limit)
(unchecked-remainder (inc (* p z)) limit)
(unchecked-remainder (* S S) (long 50515093)))))))
On May 3, 1:21 pm, Brian Watkins <wildu...@gmail.com> wrote:
> Any ideas about this?
>
> On May 2, 1:44 am, Brian Watkins <wildu...@gmail.com> wrote:
>
>
>
>
>
> > I'm trying to speed up computing terms of a simple recurrence where
> > the terms are computed modulo some value each iteration,
>
> > (defn NF-mod-limit [p q limit]
> > (loop [n 0, nf 0, z 0, S 290797]
> > (if (= n (inc q)) nf
> > (recur (inc n)
> > (mod (+ nf (* (mod S p) z)) limit)
> > (mod (inc (* p z)) limit)
> > (mod (* S S) 50515093))))))
>
> > So I added in some type hinting,
>
> > (defn NF-mod-limit [p q limit]
> > (let [p (long p) q (long q) limit (long limit)]
> > (loop [n (long 0), nf (long 0), z (long 0), S (long 290797)]
> > (if (= n (inc q)) nf
> > (recur (inc n)
> > (long (mod (+ nf (* (long (mod S p)) z)) limit))
> > (long (mod (inc (* p z)) limit))
> > (long (mod (* S S) 50515093)))))))
>
> > But it doesn't run any faster. Also it doesn't work without casting
> > to long within the recur. Is that maybe a problem with mod and
> > primitive arithmetic or does this simply not speed up any more in
> > Clojure?
>
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