And the plot thickens:
This:
(defn convert-image [#^bytes cpuArray]
(let [unchecked-add clojure.core/unchecked-add
len (int (count cpuArray))]
(loop [i (int 0)] (if (< i len)
(let [
b (byte (aget cpuArray i))
g (byte (aget cpuArray (unchecked-add 1
i)))
r (byte (aget cpuArray (unchecked-add 2
i)))
a (byte (aget cpuArray (unchecked-add 3
i)))]
(aset-byte cpuArray i a)
(aset-byte cpuArray (unchecked-add 1 i) b)
(aset-byte cpuArray (unchecked-add 2 i) g)
(aset-byte cpuArray (unchecked-add 3 i) r)
(recur (int (unchecked-add i 4))))))))
vs this.
(defn convert-image [#^bytes cpuArray]
(let [len (java.lang.reflect.Array/getLength cpuArray)]
(loop [i (int 0)] (if (< i len)
(let [i2 (unchecked-add 1 i)
i3 (unchecked-add 2 i)
i4 (unchecked-add 3 i)
b (byte (aget cpuArray i))
g (byte (aget cpuArray i2))
r (byte (aget cpuArray i3))
a (byte (aget cpuArray i4))]
(aset-byte cpuArray i a)
(aset-byte cpuArray i2 b)
(aset-byte cpuArray i3 g)
(aset-byte cpuArray i4 r)
(recur (unchecked-add i 4)))))))
The first function takes forever; the second MUCH faster.
Upon disassembling the byte-code of the two compiled functions, it
does seem like the + was not being inlined.
Since the method of reassignment doesn't preserve the metadata, this
makes sense.
However, my new, modified function is still around 20 times slower
than the java version :(
I still don't understand what's slowing me down, but I'm much happier
that I can get within 20x of java instead of 20000x
thanks everyone.
sincerely,
--Robert McIntyre
On Fri, Jan 28, 2011 at 1:07 PM, Ken Wesson <kwess...@gmail.com> wrote:
> On Fri, Jan 28, 2011 at 12:55 PM, Benny Tsai <benny.t...@gmail.com> wrote:
>> It seems that 'unchecked-add' returns a primitive (note that in the
>> first version, 'recur' happily accepts the return from 'unchecked-add'
>> without coercion), but when 'unchecked-add' is bound to a new name,
>> the return gets boxed.
>>
>> Is this the correct interpretation, or am I missing something?
>
> It's correct. Clojure's compiler inlines certain functions, including
> clojure.core/unchecked-foo and, when the arity is 2, clojure.core/+ --
> but not a bare, un-qualified +, which might (or might not) at runtime
> refer to clojure.core/+ or clojure.core/unchecked-add or whatever.
>
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