Hi guys,
In the example below, if map is replaced with pmap, it goes twice
slower on my MBP (2 CPUs).
I believe it's probably the (reduce + ...) causing it, but I can't
explain it.
Version with map:
user> (time (pnpolytest))
"Elapsed time: 3903.533 msecs"
6000000
Version with pmap:
user> (time (pnpolytest))
"Elapsed time: 7995.565 msecs"
What I'm doing wrong here?
(defn- pnpoly [npol #^floats xp #^floats yp x y]
(let [npol (int npol)
x (float x)
y (float y)]
(loop [r (int 0)
i (int 0)
xi (aget xp (dec npol))
yi (aget yp (dec npol))]
(if (< i npol)
(let [xj xi xi (aget xp i)
yj yi yi (aget yp i)]
(if (or (= (> yi y) (> yj y))
(>= x (+ xi (/ (* (- xj xi)
(- y yi))
(- yj yi)))))
(recur (bit-not r) (inc i) xi yi)
(recur r (inc i) xi yi)))
(- r)))))
(defn pnpolytest []
(let [xp
(float-array
[+0.0 +1.0 +1.0 +0.0 +0.0
+1.0 -0.5 -1.0 -1.0 -2.0
-2.5 -2.0 -1.5 -0.5 +1.0
+1.0 +0.0 -0.5 -1.0 -0.5])
yp
(float-array
[+0.0 +0.0 +1.0 +1.0 +2.0
+3.0 +2.0 +3.0 0.0 -0.5
-1.0 -1.5 -2.0 -2.0 -1.5
-1.0 -0.5 -1.0 -1.0 -0.5])
npol 20]
(reduce +
;; Replace the nex map with pmap,
;; and things slow down
(map (fn [_]
(+ (pnpoly npol xp yp 0.5 0.5)
(pnpoly npol xp yp 0.5 1.5)
(pnpoly npol xp yp -0.5 1.5)
(pnpoly npol xp yp 0.75 2.25)
(pnpoly npol xp yp 0.0 2.01)
(pnpoly npol xp yp -0.5 2.5)
(pnpoly npol xp yp -1.0 -0.5)
(pnpoly npol xp yp -1.5 0.5)
(pnpoly npol xp yp -2.25 -1.0)
(pnpoly npol xp yp 0.5 -0.25)
(pnpoly npol xp yp 0.5 -1.25)
(pnpoly npol xp yp -0.5 -2.5)))
(range 0 1000000)))))
Thanks,
Dimiter "malkia" Stanev
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