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;; The Computer Language Benchmarks Game
;; contributed by Jim Kannampuzha
;; inspired by Jesse Rosenstock
;; modified by Andy Fingerhut (small bug where if input value n was
;; not a multiple of the number of available processors, the
;; program would hang.)
(ns spectralnorm
(set! *warn-on-reflection* true)
(defmacro eval-a [ii jj]
`(let [i# (int ~ii)
j# (int ~jj)
n# (unchecked-add i# j#)
n+1# (unchecked-inc n#)]
(/ (double 1.0)
(unchecked-add (bit-shift-right (unchecked-multiply n# n+1#) (int 1))
(unchecked-inc i#)))))
(defn multiply-a-v [agent ^doubles v ^doubles av range]
(let [end (int (second range))]
(loop [i (int (first range))]
(if (= i end)
(aset av i (double (areduce v j sum (double 0)
(+ sum (* (eval-a i j) (aget v j))))))
(recur (unchecked-inc i)))))))
(defn multiply-at-v [agent ^doubles v ^doubles atv range]
(let [end (int (second range))]
(loop [i (int (first range))]
(if (= i end) nil
(aset atv i
(double (areduce v j sum (double 0)
(+ sum (* (eval-a j i) (aget v j))))))
(recur (unchecked-inc i)))))))
(defn multiply-at-a-v [^doubles v ^doubles tmp ^doubles at-av
num-threads workers ranges]
(dotimes [i num-threads]
(send (nth workers i) multiply-a-v v tmp (nth ranges i)))
(apply await workers)
(dotimes [i num-threads]
(send (nth workers i) multiply-at-v tmp at-av (nth ranges i)))
(apply await workers))
(defmacro dot-product [^doubles u ^doubles v]
`(areduce ~u i# sum# (double 0) (+ sum# (* (aget ~u i#) (aget ~v i#)))))
(defn run-game [size]
(let [num-threads (int (.availableProcessors (Runtime/getRuntime)))
workers (vec (repeatedly num-threads #(agent ())))
chunk-size (int (Math/ceil (/ size num-threads)))
ranges (vec (partition 2 1
(take (unchecked-inc num-threads)
(iterate #(min (+ chunk-size %) size)
(int 0)))))
u (double-array size 1.0)
tmp (double-array size 0.0)
v (double-array size 0.0)]
(dotimes [_ 10]
(multiply-at-a-v u tmp v num-threads workers ranges)
(multiply-at-a-v v tmp u num-threads workers ranges))
(let [vbv (dot-product u v)
vv (dot-product v v)]
(Math/sqrt (/ vbv vv)))))
(defn -main [& args]
(let [n (if (empty? args)
(Integer/valueOf ^String (first args)))]
(println (format "%.9f" (run-game n)))
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