On Fri, Jan 28, 2011 at 10:48 AM, Robert McIntyre <[email protected]> wrote:
> I tried to convert this java code line for line to clojure to compare
> the speed differences, and boy was I surprised!
>
> public static void ConvertToAWT(byte[] cpuArray){
> // Given an array of bytes representing a c-style bgra
> image,
> // converts to a java style abgr image
> int len = java.lang.reflect.Array.getLength(cpuArray);
> for (int i = 0; i < len; i+=4){
> byte b = cpuArray[i+0];
> byte g = cpuArray[i+1];
> byte r = cpuArray[i+2];
> byte a = cpuArray[i+3];
> cpuArray[i+0] = a;
> cpuArray[i+1] = b;
> cpuArray[i+2] = g;
> cpuArray[i+3] = r; }}
>
> (defn java-like []
> (loop [i (int 0)] (if (< i buffer-size)
> (let [ + clojure.core/unchecked-add
> b (aget cpuArray i)
> g (aget cpuArray (+ 1 i))
> r (aget cpuArray (+ 2 i))
> a (aget cpuArray (+ 3 i))]
> (aset-byte cpuArray i a)
> (aset-byte cpuArray (+ 1 i) b)
> (aset-byte cpuArray (+ 2 i) g)
> (aset-byte cpuArray (+ 3 i) r)
> (recur (int (+ i 4)))))))
>
> (defn clojure-like []
> (doall (flatten (map (fn [[b g r a]] [a b g r]) (partition 4 4
> cpuArray)))))
I'm assuming you're using 1.2.0. cpuArray needs to be hinted. All the
literals also need to be hinted. Don't use aset-byte, use aset.
In 1.3.0 you no longer have to hint the literals and you can use the
*unchecked-math* compiler flag instead of redefining unchecked-add as a
local.
David
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